Small fixes for IE10

Wodo.TextEditor does still not completely work after this, but at least better then before.
Also makes ViewerJS in IE properly display ODT with annotations.

Any IE lovers around to continue this work? I somehow feel unmotivated for more ;)
Other places that use ``node.parentElement`` that should also be fixed:

https://github.com/kogmbh/WebODF/blob/master/webodf/lib/gui/ZoomHelper.js#L508
https://github.com/kogmbh/WebODF/blob/master/webodf/lib/odf/OdfUtils.js#L205
https://github.com/kogmbh/WebODF/blob/master/webodf/lib/odf/StyleCache.js#L540

It might be worth adding this to the coding guidelines (along with the note about the event object as well). That will help ensure no-one else needs to rediscover this problem.