add Readline dependency
Recent monero master builds with readline support by default, if it's installed on the system. OpenMonero build (upgrade_angular_js branch) fails if monero is built with readline support. As a workaround you can turn off readline in monero's CMakeLists.txt. 

```
[ 97%] Linking CXX executable openmonero
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `attempted_completion(char const*, int, int)':
readline_buffer.cpp:(.text+0x2): undefined reference to `rl_attempted_completion_over'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `startup_hook()':
readline_buffer.cpp:(.text+0xcf): undefined reference to `rl_bind_key'
readline_buffer.cpp:(.text+0xde): undefined reference to `rl_bind_key'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::readline_buffer::sync()':
readline_buffer.cpp:(.text+0x11b): undefined reference to `rl_end'
readline_buffer.cpp:(.text+0x124): undefined reference to `rl_point'
readline_buffer.cpp:(.text+0x129): undefined reference to `rl_copy_text'
readline_buffer.cpp:(.text+0x136): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x142): undefined reference to `rl_replace_line'
readline_buffer.cpp:(.text+0x147): undefined reference to `rl_redisplay'
readline_buffer.cpp:(.text+0x1e6): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x1f0): undefined reference to `rl_replace_line'
readline_buffer.cpp:(.text+0x1f7): undefined reference to `rl_point'
readline_buffer.cpp:(.text+0x1fc): undefined reference to `rl_redisplay'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `handle_line(char*)':
readline_buffer.cpp:(.text+0x2d3): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x2d9): undefined reference to `rl_already_prompted'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `handle_enter(int, int)':
readline_buffer.cpp:(.text+0x362): undefined reference to `rl_end'
readline_buffer.cpp:(.text+0x369): undefined reference to `rl_copy_text'
readline_buffer.cpp:(.text+0x376): undefined reference to `rl_crlf'
readline_buffer.cpp:(.text+0x37b): undefined reference to `rl_on_new_line'
readline_buffer.cpp:(.text+0x385): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x394): undefined reference to `rl_replace_line'
readline_buffer.cpp:(.text+0x399): undefined reference to `rl_redisplay'
readline_buffer.cpp:(.text+0x507): undefined reference to `add_history'
readline_buffer.cpp:(.text+0x542): undefined reference to `rl_done'
readline_buffer.cpp:(.text+0x5ff): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x604): undefined reference to `rl_on_new_line_with_prompt'
readline_buffer.cpp:(.text+0x609): undefined reference to `rl_redisplay'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::readline_buffer::set_prompt(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
readline_buffer.cpp:(.text+0x7aa): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0x7af): undefined reference to `rl_redisplay'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::readline_buffer::process()':
readline_buffer.cpp:(.text+0x88c): undefined reference to `rl_callback_read_char'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::readline_buffer::start()':
readline_buffer.cpp:(.text+0x9c5): undefined reference to `rl_startup_hook'
readline_buffer.cpp:(.text+0x9d0): undefined reference to `rl_attempted_completion_function'
readline_buffer.cpp:(.text+0x9d9): undefined reference to `rl_callback_handler_install'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::readline_buffer::stop()':
readline_buffer.cpp:(.text+0xa94): undefined reference to `rl_replace_line'
readline_buffer.cpp:(.text+0xa9e): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0xaa3): undefined reference to `rl_redisplay'
readline_buffer.cpp:(.text+0xaad): undefined reference to `rl_unbind_key'
readline_buffer.cpp:(.text+0xab7): undefined reference to `rl_unbind_key'
readline_buffer.cpp:(.text+0xabc): undefined reference to `rl_callback_handler_remove'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::suspend_readline::~suspend_readline()':
readline_buffer.cpp:(.text+0xcb5): undefined reference to `rl_startup_hook'
readline_buffer.cpp:(.text+0xcc0): undefined reference to `rl_attempted_completion_function'
readline_buffer.cpp:(.text+0xcc9): undefined reference to `rl_callback_handler_install'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `rdln::suspend_readline::suspend_readline()':
readline_buffer.cpp:(.text+0xdc3): undefined reference to `rl_replace_line'
readline_buffer.cpp:(.text+0xdcd): undefined reference to `rl_set_prompt'
readline_buffer.cpp:(.text+0xdd2): undefined reference to `rl_redisplay'
readline_buffer.cpp:(.text+0xddc): undefined reference to `rl_unbind_key'
readline_buffer.cpp:(.text+0xde6): undefined reference to `rl_unbind_key'
readline_buffer.cpp:(.text+0xdeb): undefined reference to `rl_callback_handler_remove'
/home/jaquee/monero/build/release/contrib/epee/src/libepee.a(readline_buffer.cpp.o): In function `attempted_completion(char const*, int, int)':
readline_buffer.cpp:(.text+0x10): undefined reference to `rl_completion_matches'
collect2: error: ld returned 1 exit status
CMakeFiles/openmonero.dir/build.make:130: recipe for target 'openmonero' failed
make[2]: *** [openmonero] Error 1
CMakeFiles/Makefile2:69: recipe for target 'CMakeFiles/openmonero.dir/all' failed
make[1]: *** [CMakeFiles/openmonero.dir/all] Error 2
Makefile:116: recipe for target 'all' failed
make: *** [all] Error 2
```
