Convert bool settings to SettingsFact

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

* Fix minor spelling error

* Added support for the AUAV x2.1 Flight Controller
    also removed a duplicate entry for MindPX
    from src/comm/USBBoardInfo.json

Adds entries required to correctly identify, download and flash PX4
firmware to the AUAV X2.1 Flight Controller

* Update USBBoardInfo.json

Removed un-needed fallback entries. This has been tested!

And fix broken file path to save video on windows

- Shot Interval in Survey
- Much change to time/distance calc

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

This makes it available on mobile builds

Includes ability to load params

Move battery.percentRemainingAnnounce to Qml Global

The static Fact was causes problems with Qml