Add cache browsing capabilities.

All kind of edition capabilities are yet to be implemented (e.g. reordering of currently existing caches)
although controls have already been included in the UI.
Fixed typo
Add cache groups reordering functionality
Add cache nodes reordering functionality
Reorganize cache views
Add cache group creation form
Add cache node creation form
Add cache node and group edition forms
Add drag & drop of cache nodes between different groups.
Add delete buttons for cache nodes and groups
Minor changes in texts
Merge branch 'caches-definition' into dev
Added --no-execv argument when laucnhing Celery. Workaround for Celery >= 3.0.13 bug (https://github.com/celery/celery/issues/1150#issuecomment-12102949)
Fixed HTML markup error (<pre> inside <p>)
Add on cascade deletion of ban submissions
Remove --no-execv option in celerybeat init.d script
Merge branch 'dev' (caches-definition release)