Move Collections Name into `.env`

[peblair]

Per an issue that was mentioned on Slack, we really should be able to specify the collections name used by a CPO in the .env file (because, currently, dev builds of CPO use the production version's Google Drive folder). Primarily, this line would be the the target of some Mustache-generated value.

[jpolitz]

Go for it if you want to tackle it. Though I would keep any templated globals in editor.template.html, and refer to them that way. It's (a) how all of them are done, and (b) avoids templating more files. It'll also make it easier for what Paul is doing to find and incorporate into the webpack stuff.