* Add hot key handled return indicator to DRAW_FRAME::GeneralControl() and
DRAW_FRAME::OnHotKey() and all classed derived from DRAW_FRAME.
* Add code to all GeneralControl() and OnHotKey() functions to return true if
hot key was handled.
* Call event skip in DRAW_PANEL::OnKeyEvent() when key event is not handled to
allow default menu event handler to function properly.
*) add hotkey for setting the grid origin as 'S', in board editor, module editor.
*) re-position the function interface for cursor movement from BASE_SCREEN into
class EDA_DRAW_FRAME. This is a prelude to getting rid of BASE_SCREEN or
splitting it up.