consider making all settings live

[seansfkelley]

This will also mean we don't have to lock all the settings behind a credentials test.

Things to be aware of:

• The creds should still update as a unit. I'm thinking a pair of buttons, Test Connection and Save Connection Settings next to it. But that's a little clunky and doesn't actually reduce the overhead much from now.
• We need to notify when changes are auto-saved with a nearby visual indicator.