DB interaction + inventory backend

#### Using Sequelize.js + PostgresSQL as the DB system
 * SQL will be easier to debug by writing+running queries in the console or on Heroku, vs. writing Mongoose.js code and looking at console.log output
 * joins and aggregation, which are key for minimizing redundancy in our schema, are a huge pain to do in Mongo
 * changing schema is easier in Mongo, but I don't anticipate any changes that can't be accomplished simply by adding columns

#### Inventory
Viewing, adding, editing, and deleting items are all supported (routes/inventory.js). We just need to add in a frontend for inventory management.

#### Misc.
I removed the .env file from the repo so people won't be able to use our Facebook API key. The .env file is in our Google Drive folder, so just grab it from there and save it to the root directory before running `foreman start`.