Configure new sites using environment variable file

[bennothommo]

Currently, the web installer writes configuration values to the config files. Since these are kept in source control, we should try and configure the site using the environment variable file (.env).

We had attempted this with the Winter 1.2 update to this system, but for some reason, it was failing at the config stage - perhaps because environment variables are cached in some way, so if we attempt this again, we'll need to work out a way around this.