Addition of Tagging Features for Submissions & Results Views

This is a prototype of the tagging features that will be added to the Submissions and Results view.

**Submissions View:** In this view, a tagging column has been added to the submissions table. Multiple tags can be assigned to each assignment. Each tag uses a CSS element. Additionally, when hovering your mouse over the Tag table heading, a dropdown menu appears for users to search for tags or filter by a specific tag.

**Results View:** Here, a tag tab has been added to the right pane. In it, there are two main boxes: one that has all the current tags assigned to the assignment and one that has all available tags that *can* be assigned. Below it is a quick look at the tag usage across **all** assignments. Finally, if the user is an admin, they will also have the option to add or remove tags (again across **all** assignments).

**Upcoming Changes:**
* Better tag CSS element.
* Fix of the dropdown tag list.
* Modal dialogs for Add/Remove tag in the Review view.
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