Drive: split the nuxeo-drive GitHub repository into 2 repositories: Python client and Java server addon

One for the Python client, let's keep https://github.com/nuxeo/nuxeo-drive, and one for the nuxeo-drive addon, why not call it https://github.com/nuxeo/nuxeo-drive-addon ?

Many reasons for this:

• Client and server addon should have independant release cycles, the addon following the Nuxeo Platform / the client having its own one (we now want to release Nuxeo Drive more often than and independently from the Nuxeo Platform).
• Client is Python code, not compiled / server addon is Java, compiled by Maven.
• Client artifacts are the result of a Python freeze (MSI or DMG package), deployed to the drive update site http://community.nuxeo.com/static/drive / server addon artifacts are jar built by Maven and deployed to Nexus.