Implement Categories Model

[AndrewMusgrave]

#29 References categories although a model has not been created. I don't see another issue open regarding this, but please let me know if there is.

I'll handling this while creating the rest endpoint.

[KenavR]

Thank you, I hope I find time tomorrow to merge your PR and specify the models. If not, definitely on Wednesday.

[ozgunbal]

In current implementation, categories is set as unique. According to #6, it should not be. Is it logically okey to be unique? Movie and series have a category/genre attribute, can be still unique with that condition?

[AndrewMusgrave]

Movies and series should be able to reference the category, removing the need to have more than one of a given category.

[KenavR]

Ups, I thought I answered yesterday, that was my mistake in the model, it should be unique.

[AndrewMusgrave]

Added description to the model I created in my last PR to match #6 . So this issue should be solved with my latest PR #51