Adding functionality for Remove Submission from grading pool.

This would maintain the history for deleted submissions via new database table.
TNL-900
Additionally, in order to remove the padding-left that the base LMS is adding, unfortunately it means that a padding rule needs to be forced using !important. To .openassessment .list--actions, the padding-left action needs to be forced to be !important to match the padding/spacing in the UI mocks. - (reference: https://www.dropbox.com/s/lxkl9k32hlu7k9d/ora-important-rule.png?dl=0)