[2.0] Fixing ClassMetadataExporterTask to use existing configured annotation driver for given path instead of re-creating it

[2.0][DDC-236] Enhanced unique constraints to support names. Fixed general issues on XML and YAML exporters. Fixed issues on XML, YAML, Doctrine 1.X and Annotation drivers.

[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

[2.0] Added functionality to convert a Doctrine 1 schema to Doctrine 2 to help users with upgrading. Lots of other small bug fixes and changes.

[2.0] More work on ClassmetadataExporter and ConvertMappingTask for converting mapping information between various formats