Improving error handling on Model.list().
Adding ability to pass a suffix to Extension.scan().
Improving example extension types descriptions.
Improving extensions scanner. Renaming Extension.scan() to Extension.scanExtensions() and implementing a more generic Extension.scan().
Initial "dependency injection" work. Making sure extensions are added respecting dependency order.

Removing scanExtensions() static method from Extension class. Adding a similar loadExtensions() method to Prana application class and making it add extensions automatically. If there are missing extensions it will fail.