Followup cf1e167: unbreak SurfaceWidget

SurfaceWidget needs to pass a reference to the surface
when setting up the toolbar.

Also reverse the order of operations in the ve.ui.Toolbar
destructor. Individual tools' destructors call .getSurface()
on the toolbar, so we have to unbind the surface after
destroying the tools, not before.

Change-Id: I5005a33be44abf062608fad0ac52c41e135e6ee7