Separate mouse event handlers for GL3D bar chart.

They are just skeletons for now.

Change-Id: I7e5e95ad8a2809125cbcf3affd17e663aafa99b0
Several more Window events to intercept for the GL3D chart.

But not painting or resizing events. Those are generic enough that no
branching is needed.

Change-Id: I0fb186da61c583c5326d2608b2153aced3fab77b