[MWF] Use full width for measuring text

Previously we applied the padding twice.
[MWF] Use full available height for text

This is especially relevant if we have to shrink the width because of
padding. In this case it is possible that MeasureString calculated that
the string would fit in one line, but because of padding we reduce the
width. If the button is large enough we want to display additional lines
even if MeasureString told us we only need one line.
Merge pull request #1348 from ermshiperete/ImproveButtonTextLayout

[MWF] Improve button text layout