Update README

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

This reverts commit 233a1716.

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

Change so MainWindow handles its own deletion, and deletion of other UI objects to allow for closing when the MainWindow is closed, regardless of if other windows are open.

Change for the new RC calibration widget, still needs an if/else to load the old one for unsupported systems

Changed OS X build instructions to force qmake to generate a Makefile instead of xcodeproj files.