Mutation observers for HTML, CSS panel + misc fixes

Makes the HTML panel use mutation observers, except for "break on *".

Also includes use of mutation observers in the CSS panel ([see issue 6176](http://code.google.com/p/fbug/issues/detail?id=6176) - might need some discussion) and some random fixes to lib/wrapper because I'm too lazy to separate things.

html/ FBTests pass locally, at least.