Nimble downloads package before checking if the same version is already installed
When performing the `nimble install ...` command, the order of operations appears to be:

1. download source of package
2. prepare package for install (create a directory for the package with the relevant contents from the source repo)
3. check if package version is installed

where I believe the order of operations should look more like this:

1. get list of installed versions of the package
2. get list of remote versions of package
3. compare if the latest version of the package is already installed

I believe this should be the correct order as it doesn't require the download of a repo of unknown size only for the user to then find out that the latest version is already installed.


Edit:
i forgot to include the version of `nimble` i am currently using:
```
nimble v0.11.0 compiled at 2020-03-11 21:40:19
git hash: 5bb795a364a431f897c3864186dbe1aa138c85b9
```
and it was compiled against `nim` version:
```
Nim Compiler Version 1.0.6 [Linux: amd64]
Compiled at 2020-01-23
Copyright (c) 2006-2019 by Andreas Rumpf

git hash: 89b39ee8fe271d0e1b75c15a4c6cf82eb9c13aea
active boot switches: -d:release
```