Completion of Tag & Results View

The tag feature is almost completely implemented for the Tag and Results views. The current features have been implemented:
* Tags can now be assigned to submissions.
* Tags can now be removed from submissions.
* Tags can be created, edited, and deleted.
* Tag lists can be downloaded in CSV and YML.
* Tag lists can be uploaded in CSV.

The following features are outstanding:
* Further testing.
* Delete dialog in Results view.
* Uploading YML tag list.

Testing has been performed on all the implemented features.
Useless assignment to variable - `file_output`.