commission payment workflow overhaul

[zkat]

Fixes: #428
Fixes: #424
Fixes: #422
Fixes: #446
Fixes: #425

This PR implements the new commission payments workflow, per the discussed redesign, module the Works feature, which is handled by #232. The $20 limit stuff will be handled by #452 instead of here.

• New status box
• Terms link in comm and request
• Final Invoice button + menu
• Release All Deposits + confirmation/verifications
• Request Deposit + menu
• Show receipt at-time-of-invoice for invoice comments
• Show amount released so far as part of the summary
• Display lock/blocked thumbnails for unlocked images for artists, too (to make it clear for them that it's still locked)
• Get old tests passing
• Clean up multi-currency commission nonsense, since commissions are only supposed to have one currency now?
• Ask for tip automatically with the final invoice (not for deposits)

[coveralls]

coverage: 45.822% (-0.06%) from 45.885% when pulling 3a60be3 on zkat/new-comms-workflow into 4d82b4f on main.