display heading and pitch
extend UIView to give the C++ side a container for new-ui content
convert WorldView heading & pitch labels to new-ui
click
use frame-relative position in WorldView.cpp calculateHeadingPitch
don't create and destroy widgets or reconnect signals every frame
early-out from UI::Label::SetText if the text isn't being changed
early-out from UI::Single::SetInnerWidget if the widget isn't being changed
lang and logic cleanup
use msg log instead
don't draw UI when DrawGUI is false
Merge pull request #3108 from dvolk/headingandpitch

Display ship heading and pitch