Create a short url for documents

The full urls embeds the category and organisation slugs, which
generates too many queries when iterating over a list of documents, e.g
on a related_documents field.
Save 1 count query
Redirect to full document url view
Add revision utility functions in model
Cache attribute to prevent duplicate queries
Move favorite update in view.get() function

This update was made in the get_object() method, but this was generating
duplicate queries.
Add revision form in document detail template
Initial document keys where not real slugs
Add toto file to .gitignore
query optimizations
Save a useless query
Delete useless css rule
Add titles in document form
Activate missing fields in metadata form
Add revisions in edit form