Allow extensions with vendor name

With this pull request you can also build extensions with the folder order vendor/extension
Issue #164
But it lacks of compability to the generator. The *Extension.php Main file has the wrong class name.
Example:
package name -> pgnonick/test
class name -> Pgnonick/testExtension.php

Main path in extension.php is also wrong: Pgnonick\\Test\\Pgnonick/testExtension

Better:
class name -> TestExtension.php in the namespace Pgnonick\Test
main path in extension.php: Pgnonick\\Test\\TestExtension