Created enabled bundles import method

Allows to show that bundles can still be manually registered (for
example bundles that have a dependency on the AppKernel).
Refactored getConfiguredBundles

* usage of convenient wrapper Yaml::parse
* combined usage of:
  * instanciator: anonymous function to convert fully qualified
    classnames into instances
  * array_map to apply instanciator
  * array_merge for restricted bundles