VOMS authN middleware.

Module to perform external authentication based on VOMS. It is able to
autocreate users if they do not exist. See doc/source/voms.rst for
documentation.

Change-Id: I38eacbdc5c117bfe38cedb40833cd48cfd241b9e
Fixed unit tests

Change-Id: I0078088c2a8d7855266686da49731a78bb68ad90
Check for boolean True to see if VOMS is applicable.

Before it just checked that 'voms' keyword was present, not it will
check that it is set to the boolean True (added a unit test for this).
Also update and improve the documentation.

Change-Id: I514570edac86d6e830a3d1df2fb35e39ee537bec
corrected name of voms.json
Change backend to be aligned with API

 - Allow the possibility to get unscoped tokens
 - Move user_id to UUID on voms backend
 - Added tests against the token backend
 - Updated documentation

Change-Id: If1deb76c9f8a58170a8965f2334642e8d19b7179
Added setup.py file and updated documentation.