problem:
in src/ui$/HUD.cc copyImage(UASInterface* u): u->getImage() was called twice. The first called already erased the buffer.

changes:
src/ui/HUD.cc: copyImage(UASInterface* u): instead of getting the image a second time, we take the one we already fetched

Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

also adds AMSL output in ft

Removing UASes now returns the UI to an almost pristine state. This was done by altering the activeUASSet signal so that it can emit a NULL UAS. Crashes may still exist in autopilot-specific code.

Removed OpenGL dependency in HUD, merged in HUD from Soren Kuula and config changes from Michael Carpenter

Removing UASes now returns the UI to an almost pristine state. This was done by altering the activeUASSet signal so that it can emit a NULL UAS. Crashes may still exist in autopilot-specific code.

Impl. Lorenz suggestions wrt one velocityChanged, altitudeChanged, speedChanged signal per reference frame. Impl. CDI on compass disk.

The HUD is now theme-aware. Unfortunately it still has some coloring bugs and doesn't support changing themes at runtime. Not sure if the latter is a show-stopper however.

Fixed a number of bad bugs in the HUD, will need a bit more write / SVG rewrite to make it pretty, but is substantially more accurate and reliable now