Only use logic mapping during paint for col/rowbars.

Change-Id: I12e59b94f73eea18d0d407d9898c59b8d68eb4a2
Introduce GetScrPos to ScGridWin.

The ViewData version still uses old scaling and is therefore problematic.

Change-Id: I42d904251d8bbe1804fd099306d54045c9cf0c92
Introduce GetScrPosPix/Logic in place of plain GetScrPos.

We should make it obvious what we're actually getting, and get
the most appropriate version as necessary.

Change-Id: I45a2eb6ddc2e24993c2dfdfeea35e831e822adc3
Col/Row Headers: use correct scaling.

This makes the headers behave quite well, still some issues
with lines occasionally missing etc. though.

Change-Id: Iecbef29afec877e906a322188bc2280018fc8319
TEMPORARY: use a different paint rect.

Change-Id: I5fca6c31d0a526aa0a393d2bf68aeda81962ae36