Generalize SchemaManager Db Column to Doctrine Type Detection

Currrently the Transformation from each Database Column to a Doctrine Type is hardcoded in the SchemaManager. This code has to be generalized and moved to the Platform so that people supplying custom doctrine types can overwrite this. The API for this sould look like:

$platform->registerDoctrineType($doctrineTypeName, $dbColumnType)

This way we could supply all the defaults using this API and give users the ability to overwrite or extend it based on their needs.