Sprite widget mouseevents

[luxigo]

In order to handle mouseevents properly with sprite based widget.object3D there's quite some work.

The sprite mesh has an arbitrary size and shape which is not matching the sprite material (ie: texture with alpha layer)

Therefore it is not relevant to use the sprite mesh for mouseover detection with raycaster in widgetList_get_mouseover_list(), nor for offscreen picking in widgetList_filterHoverList()

Also, it looks like it would be bettter to use a widget.object3D list with raycaster.intersectObjects() in recursive mode instead of "camera.meshes" list in method widgetList_get_mouseover_list().

Moreover there is an issue with "mesh.parent.name" sometimes not set for sprites in widgetList_filterHoverList()