Use MutationObserver if available

This will need to be tested in multiple browsers:

- [ ] Chrome
- [ ] Android Browser (not Chrome)
- [ ] Firefox
- [ ] Safari
  - [ ] Mac OS
  - [ ] iOS
- [ ] IE
  - [ ] IE 8
  - [ ] IE 9
  - [ ] IE 10
  - [ ] IE 11
It gets rid of the slight flicker when widgets load :P  (On Chrome at least.  Should do the same for other browsers that support it, which is [nearly all current browsers](http://caniuse.com/#feat=mutationobserver))