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.

This reverts commit 52160d80.

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.

No more user prompting

Use component id from heartbeat

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

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

Instead us a Toolbox concept which hangs off of QGCApplication

Link ids were being used interchangeably with the mavlink channel for
the link. Link ids handed out as a numerically increasing integer. Once
the counter went past MAVLINK_COMM_NUM_BUFFERS all hell would break
loose and cause memory corruption.

Also many LinkManager API changes to further isolate all link
management inside LinkManager.

Moving methods from MainWindow to QGCApplication so that more things
can run without a window. Helpful for testing.

Plus a large number of other changes to allow for orderly shutdown of
objects without crashes or asserts. This is need for unit tests to
create/delete global state around every test.