Accepting the mouse events breaks moving the window by dragging
the title bar. The reason is that it eats the mouse event and
by that never reaches KWin core to perform the movement.

Other mouse buttons need to be accepted for handling the window
operations. Also we need to listen in general to left mouse
button for the double click operation.

BUG: 304249
FIXED-IN: 4.9.1
REVIEW: 105784