WebDAV management

[florian]

The WebDAV share must be managed by Amanite.

This include:

• dynamically set the .htaccess to define who is authorized to do what
• manage the password access (directly by django or with a password file)

The WebDAV access must be enabled (or not) in the profile.
The synchronisation must be done only if the WebDAV access is enabled.
When it's just enabled, we must take care of the merging of existing data.

Depend on #3

[florian]

Done: apache auth through django (no passord file needed)

Also need to be done: sync from foxmarks only if newer timestamp (now possible thanks the profile)