Send a CLEAR_ALL when mission is empty
Assert when requested waypoint is out of range

 - additionally, silenced a number of unhelpfully verbose logging
messages
Correctly handle reading of an empty mission
TxMissionItem/ClearAll share final ack handling logic
Settings and Follow Me moved to bottom of sidebar

- follow me button disabled
Merge pull request #94 from fightingwalrus/igcs-153-disable-followme

Settings and Follow Me moved to bottom of sidebar
Merge pull request #92 from fightingwalrus/igcs-145-zero-waypoints

Igcs 145 zero waypoints
Merge branch 'master' into igcs-100-logging