default config
Taskopen creates the default config file on its first execution. In situations where taskopen shall not be executed in the user's home environment (e.g. testing or packaging), the default config must be overriden with settings that do not reference $HOME. Although this is possible at the moment, it is not straightforward to obtain a config file without running taskopen in the first place.

In order to simplify the above use case, the following changes should be applied:
* taskopen should be deployed with a default config (in a system directory)
* taskopen should ask the user (if a config file does not exist) before creating and filling it with the default values