mouse button and key press callbacks in the fltk backend

[Shai Ayal]

Hi all,

I just pushed http://hg.savannah.gnu.org/hgweb/octave/rev/9cdd6c8c05a4 which implements mouse and keyboard callbacks for the fltk backend. 

The following figure callbacks should now be functional:

windowbuttonupfcn, 

windowbuttonmotionfcn, 

windowbuttondownfcn, 

keyreleasefcn, 

keypressfcn 

In addition, the currentpoint property for figure and axes objects is updated with the mouse position:

As a demonstration for the use of these properties and callbacks I implemented the ginput function for the fltk backend.

Shai