Prevent shutdown ordering crashes

Plus other auto connect bug fixes

Was failing on slower ArduPilot boots. Also could fail on PX4 boots
which required px4io flash on boot.

- Also fix vehicle selector dropdown in toolbar

Refactored PX4 radio config to work with both PX4 and APM

This guarantees we are past bootloader on all OS. Window tends to not
detect bootloader, connect to it and then get confused.

Windows OS doesn’t disconnect port when you pull plug on USB. This
caused all sorts of problems with previous logic. New logic handles
this correctly.

- 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