Make gvacommon distributable

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

.gitignore

@@ -1,5 +1,8 @@
-.*.swp
+*.egg-info
 *.pyc
-.ropeproject/
-coverage-report/
+.*.swp
 .coverage
+.ropeproject/
+build/
+coverage-report/
+dist/