Small fixes refactors

Includes the following changes. Also merged changes from#996 up to #c41999b

- Remove Gravatar libraries and references to them in both code and templates (merge too PyBossa/crowdcrafting-theme#47 and PyBossa/pybossa-default-theme#55).
- Fix and completes some tests in auditlog authorization module.
- Default Sentinel module to use a normal StrictRedis connection when used outside of an application context.
- Create rq.Queue objects explicitly.