Add spec for the CustomDynamicItemViewController

Also removes the CustomDynamicItemViewController stub file and the
ExamplesTableController link to the stub in prep for Will to complete
this VC.

Refactors CustomDynamicItemViewController to allow for unit tests.
Deletes CollisionsGravitySpringViewController Stub

See previous commit msg for other details of this push.
Merge pull request #24 from dennismajor1/gravity_spring

Did rake clean --all and tested VC's