Add a __version__ key to vp and n3fit

Created by: scarlehoff

There are so many corner cases... but I guess we can consider burning down a string only upon deploy and call the git code otherwise.

I am missing a very important use case* I don't know how to go around: I have my repository in one folder and run the code from a different folder. So I cannot just "git it". Rely on installing the files in development mode doesn't work either. I can burn, from setuptools, the path to git...

Anyway, I'd love any ideas for the previous situation.

For the burning the version on the conda package I think what I did is ok (with a bit more logic to go around cases in which there is something written in the __init__) as well as for when the code is ran inside the repo. Any comments?

*it is very important because it is probably the standard case in clusters

Closes #275 (closed)