Added API CRUDS routes for Accounts, Categories, Transactions

Summary:
The main changes in this commit were to add API endpoints for CRUDS
actions on accounts, categories, and transactions. This included adding
routes and DB models.

Test Plan: Still working on API documenation for testing

Differential Revision: http://git.simplebudget.net/D1
Merge branch 'master' of github.com:frahmj/simple_budget