Resolve "Test submission for scripts"
Changes
- Refactored the way submissions are stored. Now instead of having a 
SubmitSubmissionThere is aTestSubmissionandCoreSubmissionboth of which extend from anAbstractSubmitSubmission. ThesubmissionIdin Core for a submission is the same as thecoreSubmissionIdinCoreSubmission. - Teachers and Head TAs can now make a test submission for their script train and versions.
 
Examples
Closes #12 (closed)
Edited  by Danae Savvidi


