We actually don't need to hide it, but rather just need to make sure it remains static and unchanged while the restriction is active.

First version done: https://github.com/WikipediaLibrary/TWLight/compare/master...Samwalton9:restrict-processing?expand=1

Still to-do:

• Explicitly restrict users from commenting, in addition to just disabling the 'Add comment' button.
• Stop coordinators being able to interact with restricted users' applications
• Give superusers a warning message in the admin interface for restricted users
• Add tests

Should switch this to being membership of a group rather than a field so that we can do permissions checks, like we do for coordinators.