Add initial TOTP watch face impl

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

movement/movement_config.h

@@ -12,6 +12,7 @@
 #include "day_one_face.h"
 #include "voltage_face.h"
 #include "stopwatch_face.h"
+#include "totp_face.h"
 
 const watch_face_t watch_faces[] = {
     simple_clock_face,