Tables: more consistent use of CellPadding.x*2 and clip-rect on right-most side of non-bordered column + fix cellbg for standalone TableHeader call.

Using CellPadding.x on both sides when BorderV is off, generally most consistent and with default value (4,2) promotes at-glance visible spacing between non-bordered columns. Effectively double horizontal padding on non-bordered columns.
Made ClipRect.Max.x matches WorkMaxX which is where we'd like to go for windows themselves.
TableHeader() submit single cell bg color if not already submitted as a full header row.
Misc comments/docs updates.
7 files changed