Fixed the core MAVLink receiver. Among other things, it wasn't accounting for fragmented messages.
Fixed code that monitors messages received (and lost)
Added a section within the MAVLink panel to show the current status (for the current vehicle)
Remove some old, unused exposed interfaces

* 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.

Still does not support multi-vehicle

This reverts commit 52160d80.

This is important to avoid having QGC hijack links that are active (we read 2000 bytes!) but are definitely not MAVLink. This can have nasty side-effects, e.g. if we would talk to an LTE modem in a laptop or alike.

This extension introduces a complete version handshake mechanism which will detect wether the vehicle AND the complete link / routing infrastructure support MAVLink 2. If they do, QGC will switch to the highest protocol version supported by all connected vehicles. If a new vehicle connects, it will re-negotiate the highest possible version. This means that we error on the side of compatibility, which later can be easily changed.

Remove/comment off debug output pollution

Fixing the telemetry RSSI indicator.

Instead of hardcoded "QGroundContorl" strings

This makes VehicleComponents reusable from core plugin without
requiring override of prerequisiteSetup

No more user prompting

Convert bool settings to SettingsFact

Use component id from heartbeat

Prevent shutdown ordering crashes

Forcing QGC to use Mavlink V2 if vehicle supports it.

No signing support yet

_finalize methods need information which is not available if all you
have is a mavlink_message_t