parentElement is not defined on non-Element nodes in IE10

To have a "blanket rule", just use parentNode everywhere to prevent future problems,
as it is equivalent to parentElement for all practical usages.
navigator.language does not exist on IE10, so check for it as well
Handle IE10 obv. destructing event objects once the event handler is done
Merge pull request #718 from kossebau/smallFixesForIE10

Small fixes for IE10
Be more verbose in the About dialog of ViewerJS, not on toolbar