Resolves#330
After loading the `config/config.php`, Pico proceeds with any existing `config/*.config.php` in alphabetical order. The file order is crucial: Config values which has been set already, cannot be overwritten by a succeeding file. This is also true for arrays, i.e. when specifying `$config['test'] = array('foo' => 'bar')` in `config/a.config.php` and `$config['test'] = array('baz' => 42)` in `config/b.config.php`, `$config['test']['baz']` will be undefined
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