Allow reviewers to override minimum requirements for an app (bug 862467)

This allows reviewers to override minimum requirements when pushing an app to public, like they can already do for devices.

Note: The alternative was allowing them to access developer pages for this app, but this made permissions checks all over the place and increased complexity greatly, so I gave up on that path. For posterity, the WIP (not working for hosted apps) branch for that version is at https://github.com/diox/zamboni/tree/reviewer_edit_features_profile