swpagerelsize ui: fix height percent value

The problem was that SwFEShell::CalcBoundRect() expected that the same
relation is used for width/height, don't assume this.

Change-Id: I6c7a968874513299757401341ca9b54206116203
swpagerelsize ui: implement remaining height support

Change-Id: Ia603c4ac6c8e9e049473904203d2c471f03ce8a5