Rewritten reftest analyzer from XHTML to HTML5

The reftest analyzer was in desperate need of some love and attention. This patch does the following:

- Rewrite the reftest analyzer from XHTML to HTML5
- Move CSS and JavaScript into their own files
- Style the reftest analyzer a bit better: clean colors and the same font as used in PDF.js
- Adhere to the style guide as much as possible (for example: using two space indents everywhere)
- Make the reftest analyzer work in Safari: fixes https://github.com/mozilla/pdf.js/pull/4318#issuecomment-35807411
- Fix a bug where the content under the cursor is not the content displayed in the pixel image on the left. To see this, go to http://107.22.172.223:8877/33dd9dd94b01582/reftest-analyzer.xhtml#web=eq.log, click the first result and hover over the annotation icon. Notice the pixel area not turning yellow in the current reftest analyzer.

Note that my goal was not to completely rewrite the reftest analyser, but only to address the most important issues.