Use `git clone --recursive` when suitable
Add displaying submission limits in CWS
Do not show negative numbers for remaining submissions.
Allow admins to enable/disable workers from AWS
Always ignore results from disabled workers

Not doing that had the side effect of re-enabling a disabled worker
when it reported a finished action. This is unexpected wrt timeouts,
but it would be easy to trigger now that admins can disable workers.
Fix closure in switching questions page
Add new author
Decouple user from contest; Allow unassigned tasks

This commit changes the DB structure in order to allow users to
participate to more than one contest.
Split loader interface; Update italy_yaml loader

This commit splits the loader interface in three interfaces:

 - TaskLoader
 - UserLoader
 - ContestLoader

For example, it's now possible to store users in the italy_yaml format
and tasks in the polygon format.