Radio Protocol Improvements, Tracking GPS Time, Recovery Script

This pull request adds four disjoint features:

- SBP MSG OBS: A new MSG_PACKED_OBS that is 50% more efficient than previous, along with new 
- TIMING: Track the current GPS time using the onboard clock, enables timing.h:get_current_time()
- SBP Piksi: Reporting UART throughput in KiloBytes/sec
- Recovery Script: A Python script that resets the USB UART to default settings.
Rename to old_obs_callback?