Fix bug where QGCComboBox { model: ListModel would not work correctly

Update to the QGCComboBox to use a textRole in the case where it's availble.

Some small theme colour fixes.

Updating the items to be inline with the theme.

This is a small experiment into creating a custom theme for QGC.

Add gimbal to external control signal

Update all files that use a QML Menu item to QtQuick.Controls 2.4 to solve the issue of a menu showing up in random places on Android.

Move PreflightCheckList to custom builds only. The model, which used to be implemented within BuiltinPreFlightCheckModel is now within the control itself. It is up to the implementer to define a proper model.

Fix height

Fix typo

New qml base log replay status bar

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Restored FirmwareUpgrade.qml as it was beyond repair. Also fixed some issues that were present in the original, master version.
Added "hasAPMSupport" to QGroundControl global control. This is to determine if APM support is enabled or not.

When the item is not visible, the width and height are not valid,
resulting in wrong output values
Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Fixed places where the font family was not being defined (therefore using the default system font)

Save/Restore stream rates. Auto flight mode support

Use regular sliders

PID Tuning rate adjustment