Add better package entry points for configuration values.

In a package method:

```PHP
// Filesystem config
$this->getFileConfig()->get('group.item');

// Database config
$this->getConfig()->get('group.item')
```

Filesystem package loading hierarchy for group 'test':

* `/packages/your_package/config/test.php`
* `/application/config/generated_overrides/your_package/test.php`
* `/application/config/packages/your_package/test.php`