add a VclViewport

like GtkViewport so that the scrolled region will be clipped,
which also has the side-effect of stopping glade clobbering
the non view-port scrolled .ui files on editing

Change-Id: Ic64174b3a35b77f068e0085cdc7721aeb33f1d82
rework RID_TP_GENERAL conversion to make widgets visible, etc.

Change-Id: I93e30198e27631ad4a6865fd202af16094c26a41