Add IntervalFileOutput

Buffers at least the configured amount of seconds of video and audio
packets and writes them to a new file when SaveInterval is called
Streamline (settings) hotkey handling

This moves all hotkeys that were accessible in the audio/publish
settings panes to a new hotkeys settings pane

Also makes the push to talk hotkeys behave like all other (settings)
hotkeys, i.e. as long as a hotkey is configured the hotkey is active
Add Save Interval support to UI/recording logic
Save complete segments