This commit performs a lot of changes to make gvacommon properly
distributable:
- add a setup.py
- move code into a module directory
- add a __version__
- add a README.rst and AGPLv3 license file (COPYING)
- specify the licensing in file headers
- move tests into a submodule of gvacommon and split tests for different
modules into separate test modules
- get rid of django-braces dependency
- adapt setup.cfg to the new directory structure
- ignore build and dist directories
