Always send MISSION_ITEM_INT to ArduPilot

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

Retry in all the right/possible places. Don’t freak out about things
coming in unknown sequences.

Instead us a Toolbox concept which hangs off of QGCApplication

- Fixed bugs found to unit test

- fix bugs found by test
- Implemented Mock mission item protocol in

The goal of this first installment is to organize the code a bit so it's more readable,
clean up a bit of left over cruft, and manage link configurations (and links in general).

Handy for testing without a real board

Working on better simulation implementation, fixed a bug where the port handle was not fully released