Update approval process & inbox UI [Do not merge]

Supersedes https://github.com/unikent/programmes-plant/pull/328

- [x] Add new inbox UI (one button plus review page with full diff view)
- [x] Support for basic diff from live restored
- [x] Reject action removed
- [x] Refactor diff code
- [x] Use new "awaiting_review", removing need for extra status (start removing status)
- [x] Basic review -> process working
- [x] rewrite tests to test new proccess
- [x] remove references to now defunct "awaiting approval process"
- [x] Make pushing revision later than awaiting revisions automatically close "review" requests
- [ ] Email users who have requested versions of this revision to go live, when it goes live (maybe)
- [ ] Use language files for new views