Add tests for date related filters in the api

    Test the get api when filtering by date.
	    Add the following tests:
		    * test_date_start
			* test_date_end
			* test_date_delta_with_date_end
			* test_date_delta_with_date_start
			* test_date_delta_with_date_end_and_date_start
			* test_date_delta_with_no_constraints
		And the following helper methods:
			* create_test_data
			* _test
Merge branch '1030905-more-api-tests' of github.com:iankronquist/fjord into 1030905-more-api-tests