Using a vector to store navigation modes
Switched to using c-type arrays
Added some comments
mavlink: store last heartbeat time in telemetry_status topic
commander: failsafe_state removed, replaced with bool failsafe, navigation state and failsafe determined directly from main state and conditions
commander: modes display fixes, don't activate failsafe while disarmed
commander: added some failsafe logic
mavlink: publish telemtry status without radio status
commander/navigator: renamed FS modes to RTL and RTGS (return to ground station)
Merge pull request #1057 from achambers16/navigator_rewrite_modes_list

Navigator rewrite: create list of navigation modes
mavlink: only publish telemetry status from GCS
Merge branch 'navigator_rewrite' into dataman_state_nav_rewrite