Add support for Linux and experimenting with settings (there are "set" but no "get" options for them though)

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.

Add support for specifying fixed RTK base position

AirspaceManager is now exposed by QGroundControlQmlGlobal instead of Vehicle (available all the time)

Replacement code to speed up work on the map and fighting mistake 'manual control lost' when connected joystick with armed UAV

This allows for better multi-vehicle testing

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

Convert bool settings to SettingsFact

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

Prevent shutdown ordering crashes

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

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

Move battery.percentRemainingAnnounce to Qml Global

The static Fact was causes problems with Qml