chore(demo): update demo to include animations
refactor(collapse): use ngAnimate

- Animations are now opt-in, include ngAnimate to see collapse
  animations

- ngAnimate handles initial state and doesn't animate if first
  reflow hasn't occurred.
  https://github.com/angular/angular.js/commit/cc5846073e57ef190182026d7e5a8e2770d9b770

- Tests may need more work. Right now they test for 'in' class.

Closes #1274