Problem/Motivation
Media entities are revisionable but it's not possible to:
- view a revision
- revert to a revision
- delete a specific revision
- see a diff of revisions, if the contrib Diff module is enabled.
Proposed resolution
Introduce the revisions tab, like we have it for node.
Remaining tasks
Also introduce 'view all revisions', 'revert all revisions' and 'delete all revisions' permission.
