Normalize license headers of editor/benchmark/tests/firefox-addon/viewer source files

* remove @license tag, for consistency with library source files
* use copyright@kogmbh.com email address everywhere
* remove "additional permission", to be added only to released stuff
* separate license header by empty line from following content
Add license header also to all CSS and big test data xml files
Merge pull request #622 from kossebau/moreHeaderNormalization

Normalize license headers of editor/benchmark/tests/firefox-addon/viewer source files