Solved when JSON returned is empty

When there is no elements requested the JSON returned is empty,
in this case the extract function in the RESTAdapter must return
a empty array.
Merge branch 'wip/ember_migration' of https://github.com/MateusZitelli/traintool into wip/ember_migration

Conflicts:
	frontend/app/adapters/traintool_rest.js
Test routines working

Until the moment there is only the test to verify if a
exercise is created correctly. To isolate the tests
from the REST api a clone script from the app is generated
with a localstorage adapter instead of the RESTAdapter.
Then this other version is added for the qunit test.
Created new test for exercise creation

The tests now verify all input fields and if the
exercises still in order.
Merge pull request #25 from MateusZitelli/wip/ember_migration

Created a isolated adapter for tests and some tests routines