Cherry pick joystick fixes from stable and fixup merge

Debian doc updates

Cherry pick joystick fixes from stable and fixup merge

Add return in CustomFirmwarePlugin::hasGimbal

Since Ubuntu deprecated trusty, the TravisCI build will always fail
as it is unable to download packages against Ubuntu 14.

Add information for building doxygen documentation
on debian and fix for hardcoded path for dot.

remove warning caused build failure

Compiler warnings clean up

First run prompts

More warnings cleanup
Android fix
More
More
More
Fix typo
Update android compiler warnings
Fix android compiler warnings
More android compiler warnings

Modified support for multiple first run pages. Added first run for offline vehicle settings.

Toolbar: Visual tweaks

VIsual tweaks

Cherry pick stable fixes

FactMetaData: Add custom validator support

Add custom validator support

Cherry pick stable fixes

Turn warnings back on, silence warnings we can't fix

Introduce gimbal yaw visiblity setting

Added configurable value grid to toolbar

Added configurable value grid to toolbar

Fix VTOL hover determination

Fix VTOL hover determination

ToolStrip re-architecture for encapsulation and customization

Remove old action list code

ToolStrip rearchitecture for encapsulation and customization

Re-architect toolbar for better customization, features, real estate

Fix logic of when adding Landing item is allowed

Re-architect toolbar for better customization capabilities. Also use less real estate.

Fix logic of when adding Landing item is allowed

Fly View rearchitecture

Vertical units - fix omission

Rework Fly View into separate layers which can be customized at each layer

Rework Fly View into separate layers which can be customized at each layer.