When downloading mission items from the autopilot we need to retry more
agressively, so use a shorter timeout. If we don't do this, we might not
re-request a mission item in time and the autopilot has already given up
the overall mission transfer.

This fixes the case where a mission request from QGC to autopilot or a
mission item from autopilot to QGC gets lost on the link and needs to be
requested again.

* Flight modes still not implemented. Waiting on message change.
* Also includes various cauterization of UI things which should not be
available on high latency link.

By adding a member variable for the total mission item count, we can
actually correctly estimate the progress.

Float comparison to flakey cross-platform

This prevents intersection misses on more cases

Otherwise things like gimbal angles end up on the wrong items.

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>