Made improvements suggested by https://github.com/simone-f/qat_script/pull/5#issuecomment-53637861

* Added tool icon. See https://github.com/ypid/opening_hours.js/commit/64dd4fe0db6f1f071cfe7a8498d98a25c08139a2
* Applied patch from @simone-f.
* Using HTML tags for newline in user message.
* Resized and redesigned markers.

Other improvements.
* Removed proof_of_concept.