One python package

I did the following:

• moved the sources from {common,client,server}/src to src/leap/soledad/{common,client,server}.
• moved what was in {common,client,server}/pkg to pkg/{common,client,server}.
• merged the contents of the distinct setup.py, adapted for requirements.
• changed the versioneer to lookup for ./.git.
• adapted tests.
• fixed the __version__ attribute.
• removed dependency on leap.soledad.common.

What should be next steps now? Do we want to keep generating 3 distinct python distribution packages? How to do that? What else is missing? :)