Fix the use of versioneer in the context of debian packaging

Soledad uses versioneer to manage version strings. Versioneer works by having a standard way to compute version strings dynamically, and replacing the dynamic computation by a static thing upon packaging.

There are some facts that indicate that our use of versioneer is not working well with the way we are doing python packaging:

• The version string is not being returned properly when soledad server is installed from the debian package.
• The leap/soledad/_version.py file is not being replaced correctly upon debian-packaging.
  • The file provided in the most recent released debian package is the same as the one in the source repository (it should have been replaced during packaging).
  • On a manual/local debian-packaging attempt, the file does get replaced, but not by the correct one (it still gives me a somewhat dynamic calculation with some extra info).