Make it clear when a user has unsaved changes

[epheterson]

I was modifying a plugin and didn't realize why it wasn't taking effect when I relaunched homebridge. After a bit, I realized it was because I didn't hit Cmd+S. It'd be nice if Homebridge Controller detected when there were unsaved changes, made this visible in the UI, and offered the user the option to save it, and also the option to save it / relaunch homebridge (if necessary).