Allow reporting a room when rejecting an invite.

[Half-Shot]

This adds the ability report a room when declining an invite.

Design

This:

• Changes the language in the app from "Reject" to "Decline" for invites.
• Adds a third option on the room invite view to decline & block.

Screenshots

[Half-Shot]

This code is unused.

[dbkr]

Thanks for doing the class component conversion

[Half-Shot]

Thanks for doing the class component conversion

I failed to explain why, but for whatever reason secureRandomString was giving me undefined in my tests. React's getId() was not, so this was a cheeky way to sidestep the problem a bit. I don't know if that's a bad smell, but more functional components is probably a good thing.