[2.0] Incorporated CLI refactorings. Added support to namespaces and unlimited depth namespaces. Dropped globalArguments for now, since they interfer in DAG implementation.

[2.0][DDC-122][DDC-97][DDC-98][DDC-147] Refactored metadata mapping drivers by removing the useless PRELOAD mode. Introduced ClassMetadataFactory#getAllMetadata. Classloader simplifications. Old classloaders deprecated. New Doctrine\Common\ClassLoader is almost the same as the previous IsolatedClassLoader.