A simple countdown face using movement_schedule_background_task
so that it rings, even if the another face is active
Limited to 99 minutes and 59 seconds so that the watch isn't staying
out of deep sleep for too long
Vendor code from https://github.com/Netthaw/TOTP-MCU to do the
heavy lifting of computing SHA-1 and HMAC and the rest of TOTP
Also implement a date_time to unix timestamp method