Add the admin-categories endpoint (/auth/v1/categories & /auth/v1/category/:id)

#### Introduces the following endpoints:

1. /categories
  1. POST - creates a new category
  1. GET - gets all categories
1. /category/:id
  1. GET - gets a specific category
  1. PUT - updates a specific category
  1. DELETE - deletes a specific category

#### Perform the following before testing
1. Clear your database cache from localStorage.
1. run `bower install` (for moment.js as a devDependency)