Also understand the concept of missions which cannot be edited

This was done to support both PX4 and APM flight stack with same code

Previous code was horribly wrong.

- Also added new adjustMavlinkMessage support

Too complicated supporting both modes as editor becomes more complex

Remove nigh load/save

Also much other cleanup/change

This allows for testing issues found on high dpi screen without needing
a high dpi screen. it does this by doubling the font sizes.

These use OpenGL implementation which prevented moving to ANGLE
support. Since they are rarely used they are being remove instead of
being upgrade.

These use OpenGL implementation which prevented moving to ANGLE
support. Since they are rarely used they are being remove instead of
being upgrade.

Plus more overall ui work

- New MissionManager
- Plumb MissionManager through MissionEditor
- Mission Editor supports get/set

- Only show video option if supported
- Persist settings
- Show/Hide/Add items correctly

While at it, fixed an issue with builds that have video streaming disabled.