QGCCorePlugin is currently constructed with a QGCToolbox* toolbx parameter of null. This is because at the time QGCCorePlugin (or an actual custom plugin) is constructed app->toolbox() is null.
_scanAndLoadPlugins() is called as part of the QGCToolbox constructor where all toolbox classes use the same format:
_class = new Class(app, this);

The creation of QGCCorePlugin should follow the same pattern.

The practical issue I had with this is that because the parent is not set correctly, QGCCorePlugin is not destructed when the app is closed. This means any code in the destructor is not run. (QGCCorePlugin itself has as a destructor which is currently not being called).

ADSB server support provided through new ADSBVehicleManager implemenation

On desktop (Ethernet connection), the ground unit pushes UDP directly, which makes the use of an actual "Link" not possible. Instead, I've moved all of Taisync support to a "manager" owned by QGCToolbox.
Added a Taisync settings with some basics already wired and running.

It builds clean but the resources still get messed up (loads true qml files instead of dummy ones, and it crashes...)

Break apart string of classes into their own files as all in one file became unwieldy
Expose Airspace data in a QML ready format
Split global Airspace from AirMap (Only now I figured out the reason for the pure virtual root classes)
Refactored a bunch of things to make it consistent and/or obvious

Move all airmap related stuff to its own directory

- add multi-vehicle support: each vehicle has now a per-vehicle AirMap
  object that takes care of flight creation, traffic & telemetry
- add a base class API layer so that the interface between QGC and the
  AirMap implementation is clear, and easier to change
- removes polygon upload to vehicle (needs a better solution)

Also hand carried text to speech changes from Stable to master. Plus
unit tests for that.

* Map type now set from General settings
* No map type control in maps

* Holds all the settings for the app
* Allows core plugin to override default values

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

This prevents problems with toolbox references from inside
QGCTool::setToolbox calls.

This does the following:
- add RTCMMavlink class that streams RTCM messages via mavlink
- add GPSProvider class that opens a serial device and uses the gps driver
  submodule to get an RTCM stream
- add a GPSManager class that manages the RTCMMavlink & GPSProvider classes
- implement gps driver callback & definitions using Qt
- add the GPSManager to the QGCToolbox

To test this, uncomment the _gpsManager->setupGPS("ttyACM0"); in
QGCToolbox.cc

Download Speed Tweaks (+2 squashed commits)
Squashed commits:
[ff0ef7e] Cleanup (remove OpenStreetMap)
[370fa1d] Done (+25 squashed commits)
Squashed commits:
[9f3368f] Need to check how many instances of MapEngine are active.
[d557eac] Download Optimization
[392f50a] Almost there.
Trying to optimize download.
[a49d1d2] Settings
[a94be97] Mostly there. Needs to finish options and map thumbnail.
[38d5a0b] Downloading tiles and deleting sets
[81101b9] More UI Work
[c597d4b] Downloading tiles
[a815e35] Get rid of OpenMaps
[7e177ea] More reorg
[fa6b671] Start handling create tile set
Fix signal order when creating fetch tile task
[2a31f4d] Refactoring
[268b906] Renaming things
[947d66e] Fix resource load error.
[19e2de8] Adding MapBox
[c73e627] Preparing download
[87bbf22] UI Tweaks
[3c32a86] A lot of UI code done.
[ece8ce2] Starting to deal with tiles
[7f387bc] Save tile set
[f66f343] Adding more code
[4de3418] Working
[f0cc25d] Done for the night.
[2d1d86e] Added SQL database for holding out own tile cache.
[d405a87] Convert to camel case as this has been driving me nuts.

- New mission command editor dialog
- New MissionCommands toolbox object to get command info
- Added APM mission item set

Instead us a Toolbox concept which hangs off of QGCApplication