Audio improvements

Otherwise some messages say 'System MAV 0-20' and some say 'System 20'.

Initial Battery Config

Add assert back

Couple o' changes

Should fix things.

FactTextField, when setting the value from its "text" field, was converting the value to string. This was causing (QML JavaScript) code that uses the value for computation to stop working once the user changed the value.

Support for bootloading uNode board

Moved update canvas signal to perspective load instead of hooking it to the paint event.
Added an "S" as the unit for the number of cells fact (as in 4S).

Also changed to qWarning

Remove unused Fact

Added "Advanced Settings" check box.

Created new ScreenTools exported control for QML code to obtain screen DPI factor to be used for computing font point sizes. This code used to be in the tool bar code and now is available to all QML widgets.
Moved global mouse position tool into ScreenTools as I felt it would be a place to collect these sort of functionality.
Replaced Tree used in the Safety Component from a PNG file to a SVG file as the PNG was not scaling up properly.

New Flight Mode config

Tool bar tweaks

Tool bar buttons now use QGCButton as base to inherit hover mode fix.
Made QGCButton.showHightLight into a public property so I could use it as a trigger for repainting the chevron button.

Fix hover state of Button

Also realized I don’t need __lastMouseXY

Chevron buttons in Main Tool Bar

Reduced size of the main tool bar buttons accordingly.
Connect/Disconnect buttons (and link configuration combobox) now use the default height.

Fix parameter config sizing

Use FactBinder to access facts from Qml

Passing parameters QVariantMap across C++ boundary was causing crashes
in Qt due to Qml array bugs. Referencing same Fact* across Qml boundary
in multiple QQuickWidgets caused jScript GC to crash.