WIP: EARMMS "next"

This was going to be v2.0.0 but the "old" codebase has a few more releases in it yet, so this is now just "next".

See the Trello board for progress. This MR's description will be updated as development milestones happen.

Things to note:

• Things are very broken in their current state.
• config/controllers.yml has all the controllers that haven't been updated to use the new routing system commented out - but a controller having been updated doesn't mean that it actually works properly.
• Only the email sending worker has been updated to work with Sidekiq so far - and it completely changes how the email system works, so all other code that creates emails will have to be adapted.
• The v1 keyderiv code has been ripped out, so you'll have to use v2. For development flipping-back-and-forth between EARMMS stable and this branch, keyderiv v2 support has been added to EARMMS stable, and can be enabled by setting the environment variable KEYDERIV_USE_2X=true.