Switch to mutation observer and update privly applications module.

Here I updated the privly.js module to use Mutation Observers instead of mutation events. This has significant [performance improvements](https://hacks.mozilla.org/2012/05/dom-mutationobserver-reacting-to-dom-changes-without-killing-browser-performance/). The only bad part of this pull request is that Mutation observers are [relatively new](https://hacks.mozilla.org/2012/05/dom-mutationobserver-reacting-to-dom-changes-without-killing-browser-performance/) so we will be dropping support for some older browsers. I made a similar change to Firefox, which will now only be supported from version 14.