broadcast.go: disable save button on stream startup

[Russell Stanley]

The save button on the broadcast page should not be pressed when the stream is active or starting up. If this happens the active status will be set to false meaning the health checking and chat messages do not happen. Currently, the button is disabled when the stream is active but a more robust solution is required to stop the save button from being pressed when the stream is booting up.

[Saxon Milton]

This is no longer an issue with the broadcast state machine.