Added support for nested environment config loading

This will load with respect to nested config directories in the environment. For example, config/dev/admin/app.php will try to load files in the following order:

config/dev/app.php
config/dev/admin/app.php

This allows for multiple websites within each environment scope. The environment rules would look like this.

$env = $app->detectEnvironment(array(
    'dev/admin' => array('admin.domain.dev'),
    'staging/admin' => array('staging.admin.domain.com'),
));

This should respect existing rules.