Fix validation issues in text up/down control
Refactor and clean-up new resize UI code

Now that we've got the resize UC working well, it was time to move some
code out of the control and into a public module.  Multiple functions
may need to convert between pixels and other units (cm, inch, etc), so
those functions should be available to all.

Similarly, separate width/height conversion functions were very helpful
while debugging, but really we only need one set of conversion functions
as the math is identical.