Move isEmpty and isODFNode from OpRemoveText.js to OdfUtils.
Rename OdfUtils.isEmpty to OdfUtils.hasNoODFContent,
which is much more precise.
Additionally, it should return true on textNodes only if
they are children of ODF elements.
Add property mergedParagraphStyleName to OpRemoveText spec.

* Make TextController specify the mergedParagraphStyleName
when generating a RemoveText operation. No longer let
OpRemoveText decide the merge order from the context.

* Remove the text:style-name attribute on a paragraph
if the aforementioned property is an empty string.

* Add tests for this.
Merge pull request #554 from adityab/removeText-dumbify

Fix paragraph merging issue and make OpRemoveText less magical