Create Postman Collection to Document API

There currently exists a Postman collection for the Mentor API, which is meant to provide a RESTful way of accessing and updating the Mentor collection. There is also an incomplete collection for the Organization API.

Go through the /routes subdirectory of the /backend folder and create a master Postman collection that encapsulates all current endpoints. This will go a long way towards making it easy for team members to quickly get working with the backend, and it it will also give new members a great way to start learning the codebase.

As you are creating the collection, if you notice any endpoint that seems out of place or does not follow a RESTful style, please either fix the problem or mark it down as an issue to address later.