Add mocha gem

The reason is that our old rspec-mock does not have #any_instance function yet (till later version)
Thus we use mocha in parallel, we could access the #any_instance with mocha

Very useful for controller tests

Once we bump to Rails 4, we will get rid of mocha

Refactor CceExamCategoriesController spec

[Closes #63]
Hot Fixup test controller
[Closes #63]