Switch from build-time ENV vars to run-time ENV vars

[brendoncaulkins]

This means ditching the environments folder that comes baked into Angular, and instead importing a .js file into index.html in a script tag, so it's bootstrapped. That allows us to inject variables into the window, and reference them globally.

Anytime that .js file is updated, the changes will take effect on the next reload, rather than requiring a complete rebuild of the app.