Play sound sequences asynchronously (#122)

Play sound sequences asynchronously (#122)

* buzzer sequences: first draft, does not work on hardware yet (but in simulator)

* buzzer sequences: add changes to movement.c

* buzzer sequences: add demo face to Makefile

* buzzer sequences: fix problem of interrupted sounds. Add logic for repeating sub sequences. Tidy up (move logic to watch_buzzer files, remove buzzer_demo_face)

* buzzer sequences: tidy up even more

* buzzer sequences: disable registering a 32 Hz tick callback for watch faces, so it will be used exclusively by the buzzer sequences functionality

* buzzer sequences: add callback slot functionality to watch_rtc and make watch_buzzer use it. Switch internal buzzer sequences tick frequency to 64 Hz. Revert changes to movement.c

* buzzer sequences: fix parameter sanity check in watch_rtc code

* buzzer sequences/watch_rtc: optimize calling tick callbacks in RTC_Handler

* buzzer sequences/watch_rtc: fix error in calling callback functions

* buzzer sequences: revert changes to watch_rtc logic. Instead, use TC3 as the source for timing the sound sequences.

* buzzer sequences: fix frequency of callback

* buzzer sequences: integrate changes from PR #162 (set both CCBUF and PERFBUF for correct buzzer tone)