Filter out meaningless text nodes from unit tests

Trying to write any operation tests with large XML snippets is frustrating as you must flatten the whole snippet so that the unit test comparison code won't throw false negatives due to any white space used to format snippet.

This PR modifies the unit test runner to filter out these text nodes so that the comparisons don't fail due to formatting differences in the snippets being compared.
This logic doesn't quite seem correct to me. I would suggest looking at ``isSignificantTextContent`` in ``OdfUtils`` for more robust text content detection.