Plan: CONDITION_GATE command support

Switch VideoReceiver to new API (big refactoring)

Unit Test for Survey command sequence generation

Major rewrite of Survey generation for simplicity. Also includes support for CONDITION_GATE.

Temporary use setting for using CONDITION_GATE in Patterns

Fixed 'if' typo in VideoReceiver::_makeSource method

Plan: Much better error reporting for mission transfer errors

Unit test for mission transfer error string checking

Much better error reporting for Mission transfer errors

Clean up code used only on custom builds.

fixed bug: the highlight mode is not the actually mode

Remove QGCApplication and VideoSettings from the VideoReceiver

Move the pre-flight checklist to the upper left corner of the screen.

The receiver should not touch the old videos folder, it's not
the responsible class for that.

The VideoReceiver should work 'as is', without depending on the
whole application or in the settings. This patch removes all the
hard dependencies on QGroundControl, FactSystem and Settings system
so it's easier to isolate and test the code.

Mavlink terrain protocol support

Fix incorrect passing of firmware type

Fix ArduPilot fake home position handling

Stable_V4.0 -> master sync

Fix ArduPilot fake home position handling

Preflight checklist when no vehicle is connected

Compiler switch for Survey Preset JSON generation