Add js highlighter

[AMDmi3]

Add js bit which reads fragment part of the url and highlights all elements with corresponding class. That is, for metapackage/foo/versions#freebsd it would change background of all elements with class highlight-freebsd (which can be table cells, or inline repository mentions) to light yellow. This would be useful to mark data we're linking to.

[Calinou]

This can be done with just CSS (based on this Stack Overflow answer): https://jsfiddle.net/chgwe8no/