Add signer and remove signer should add field for increasing/decreasing the required number of approvals

[Schwartz10]

See here and here. These fields should be toggle components.

There should also be some simple validation:

• when removing a signer, the required number of approvals must decrease, if the required number of approvals is going to be greater than the new number of signers
• Unless that case above gets hit ^^, the defaults for the toggle position should just be to keep the required number approvals the same