adds $.mockjax.clear() to the mixin's teardown method.
* I believe it is expected behavior by user (at least it was expected by me) that library clean after work. It is especially important in tests to keep them isolated.
* tests clean up. avoid of using third-party libraries' code in the repo. Every dependency should be resolved using bower/npm.
* using same mockjax version in tests as in dist.
Merge pull request #30 from yratanov/master

adds $.mockjax.clear() to the mixin's teardown method.