Vim: Follow PSR-2 indenting style.
App: Avoid 'unused variable' warning.

As the variable was referenced inside a string, it caused PHPMD to
complain about it being unused. Be more verbose.
Tests: Move Environment tests to a new file, #nfc.
App: Extend the register(..) method to support singletons.

This commit makes the register(..) method aware of singleton providers,
e.g., providers which may have just one instance of the class registered
at any given time.
Providers: Start hacking on a RoutingProvider, staging work...