Syntax error fixed, renamed files, added new tests, and refractored code

Fixed a minor syntax error in fields_controller.rb. On line 111 in this file, I added "format.json" before "{ render json:{}, status: :forbidden }."

Removed the :file_key field from the attr_accessible list in media_object.rb.

Changed session_id to data_set_id in media_objects.yml.

Made comments in experiments,media_objects_and users controller test files.

Added tests in all unit files for the verify the hidden field is defaulted to false.

Refractored all unit test code.

Removed all experiment files including experiments.yml, experiment_templates_controller_test.rb, experiments_controller_test.rb, and experiment_test.rb. These files have been converted to project files.

Also, renamed data_set.rb to data_set_test.rb.