Improve mozilla-accordion.js. Bug 1055830.

- Add collapse/expand callbacks.
- Add ability to programmatically create/destroy accordions.
- Add mozilla-accordion.js tests.
- Add standard GA callback JS for existing accordion pages.
- Standardize mozilla-pager.js create param to jQuery obj.
- Update accordion & pager docs.
Merge pull request #2271 from jpetto/bug-1055830-mozilla-accordion-improvements

Improve mozilla-accordion.js. Bug 1055830.