gladevcp - hal_gremlin - gremlin - introduced mouse button mode

This patch has been supplied from Steffen Noack
He added a new property to hal_gremlin to allow select the
button behavior of the mouse.

add property 'mouse_btn_mode'
0 = default: left rotate, middle move,   right zoom
1 =          left zoom,   middle move,   right rotate
2 =          left move,   middle rotate, right zoom
3 =          left zoom,   middle rotate, right move
4 =          left move,   middle zoom,   right rotate
5 =          left rotate, middle zoom,   right move

The mouse whell will still zoom the preview in every mode.
If you select an element in the preview, the selected element
will be taken as rotation center point.