Grouped logging options within General Settings

Move position of HITL to bottom. Handle no SYS_HITL param.

Changed (selected) mission item color to primaryButton instead of buttonHighlight
Adjusted some colors for better contrast
Removed a few JavaScript exceptions caused by the order of object destruction

Also pull fixedWing directly from Vehicle

Android done.

UI Tweaks for all mobile platforms.

* PX4: Deal properly with optional components

* RC map UI: Offer better defaults and user guidance

Got the new BAT_LOW_THR parameter.

all calls to qsTr are done, if I didn't forget anything,
on the PX4 QML files.
Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

Add scroll height indicators to Flickable