Create one django application for each webapp feature

The webapp code must be refactored in order to isolate each feature into a dedicated django application centralizing templates, views implementation and URLs definition.

The following features should be a django application:

• Web API (already a django app)
• Browse (already a django app)
• Save Code Now
• Mailmap
• Deposit moderation view
• Miscellaneous (badges, iframes, metrics, ...)

Those applications should also be enabled or disabled by configuration, for instance Save Code Now or Mailmap are not of interest for a SWH mirror.

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Migrated from T4398 (view on Phabricator)