Run Postgres from a Docker container

[nathansgithub]

This is a:

• [ ] bug
• [x] enhancement
• [ ] feature-discussion

Enhancement

Description

To make running the project locally easier and cross-platform, we should configure it to run PostreSQL from a Docker container. This will mean that the user won't have to set up their own instance of Postgres themselves, and there will only need to be one set of instructions that will cover all OSes. I noticed there were no instructions for running on Linux, but instead of adding new instructions and a new command, I think this is a better solution.

Implementation

• Remove loadDataMac/loadDataWin commands in package.json and replace with one command that loads the database
• Update CONTRIBUTING.md to reflect new process

[nathansgithub]

I went ahead and made a pr with these changes since it's pretty straightforward. Let me know if you want to make this enhancement!