[2.0] DDC-268 - Exchanged DoctrineException for MappingException and added missing exception method (thanks to Christian Heinrich for the patch)

[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.

[2.0] Refactoring some common code in to the AnnotationDriver and creating PhpDriver for consistancy