Allow more environments

You have described 3 environments if I am not mistaken.

So why can't you do this?

Development office                 => CI_ENV = "development"
Development production server => CI_ENV = "testing"
Production server                   => CI_ENV = "production"

Four:

Code:

Local development                      => CI_ENV = "development" // db ip: localhost, dbname: name1
Office testing                         => CI_ENV = "docker" // db ip: externalhost, dbname: name1
Production server testing subdomain    => CI_ENV = "testing" // db ip: localhost, dbname: name2
Production server real site            => CI_ENV = "production" // db ip: localhost, dbname: name1

All it would take is to remove the default case to a 503 error in the ENVIRONMENT switch, but I know changes have to be justified, so I didn't go straight for a pull request.