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.
I would say turn them back on :+1:

If we write another suite of tests that require testing animation timing and other such stuff, it's good to return jQuery to it's default state after these finish.