o Key-press event in the QGLView were ignored, as it never got the
  focus. Fix: Gain focus on mouse-click inside that view.
o QGLView: make zoom-in as well possible on '=' key. On American
  keyboards, the '=' key is right next to the '-' (Minus) key, while
  '+' (plus) requires Shift-equals.
o Provide a useful 'c' key-binding for 'center'. Very useful after
  getting lost in panning.