html summary rework

This MR contains various changes affecting the html summary of piglit.

My initial goal was to reduce the size of the html files and speed up the loading of theses file in a browser.

The 1 first commit changes the structure of the dom to use nested tables instead of a single big table. The 2nd allows to fold/unfold these nested tables:

The others reduce the html output size by either: moving stuff to the css file or removing whitespaces.

Note: the 4th commit has a big impact on file size but also on the index.mako readability so I'm not sure if it's a good idea.

The outcome of the patches is:

• html files are ~2x smaller (index.html is 6.7MB vs 12MB for a run of opengl profile)
• page loading is ~3x faster