Add Point and Size versions of convertMm100ToTwip/TwipToMm100.

There seem to be quite a few cases where the individual components
are being converted, this way we can just conver the entire
object as one.

Change-Id: I0043b6f40520d7497e6edc185187706b255f2354
Lets not roll our own twip/mm100 conversions.

Change-Id: Id1d0c2bed0359c35086d963dcfe9b765b6232b09