Addition of Tag Models and Controller

Created the models and controller for the tag object. Passing this over to @nathanychow so he can add more to the Tag back-end. 

This is a very basic introduction to the tag object. No functionality is expected from these files.

Also, @david-yz-liu let me know if I'm doing this right. It seems weird that I'm merging all these commits into the tagging branch.
Final newline missing.