Alter admin/mod keys if admins/mods are removed

[Kira Oakley]

This covers a case like the following:

1. User joins a cabal with a url like cabal://abcdef?adminKey=deafcb
2. User runs /unadmin deafcb
3. User quits cabal and re-launches
4. deafcb is once again an admin

There's also a case where Step 3 is instead "User shares the cabal uri on the top right corner and makes deafcb admin on others without intending it)".

I think the fix would be to move admin and mod keys to cabal-cli, and have the url we show on the top right update to reflect current admin/mod keys.