Fix #781: Added a `check_inplace_files` management command to remove purge the database from references to in-place imported files that don't exist on disk anymore

Fix #737: delivering of local activities causing unintended side effects, such as rollbacking changes

This reverts commit 8b47af8b, reversing
changes made to c0055b3b.

Fix #737: delivering of local activities causing unintended side effects, such as rollbacking changes

Ensures federation urls can answer to application/ld+json, application/activity+json and application/json requests