Optimized highlighting.

Old code was really inefficient if you have many `textNodes` (what is the case in pdf.js text layer). Code forced DOM change for every node separately. It should probably be using a DocumentFragment to cache things somehow and then replace at once all. jQuery is internally doing that so using jQuery on all set improves things. On my tests I got a 40% improvement (instead of 1.9 s for whole page selection, 1.1 s).
Merge branch 'highlighting-optimization' of https://github.com/peerlibrary/annotator into typed-packaging

This speeds up the creation of the Text Highlights
by wrapping all the text nodes in one step, instead
of doing a separate DOM change for each nodes.

Thanks @mitar for the patch.