Restore original rowspan/colspan rather than normalizing or overwriting with NaN

Store originalRowspan/Colspan as strings instead of numbers,
so we get the actual original value. Use the original value
if the number we're setting is not really different
(prevents normalization of "02" to "2") or is NaN
(prevents normalization of "2 blah" to "NaN").

Bonus: don't modify dataElement.attributes

Change-Id: Ic30e0d6f7bfe27c10e505b7c18fe9200f322cfc7