GRAILS-10335 - Override Grails mappings for collections when property is mapped with a custom Hibernate UserType

Fix of [GRAILS-10335](http://jira.grails.org/browse/GRAILS-10335). If the property in a domain class has a custom Hibernate UserType, then the UserType is responsible for mapping this column to the database and overrides Grails mapping of Map, List, Set and Bag types.

With this patch it's possible (for example) to map Map<String, String> to a Postgresql native Hstore column type instead of the additional table created by default by Grails.