refs #49: Refactor DatabaseUtils::to_schema and provide create_tables support for BaseValues
refs #49: cleanup
Removed _version_id from create_tables for BaseValue
Renamed BaseEntity#type to _type to reduce the possible name clashes with domain attributes
Implemented Mapper#insert for BaseValues
Clean up of Mapper#insert test
More BaseValue#insert tests
Added a layer supertype for immutable objects
Delete support for BaseValues
Merge branch 'issue49-immutable' into issue49
BaseValue#delete test with multiple identified_by attributes
BaseValue#update implemented
A bit of cleanup in the Mapper
Merge pull request #53 from mcamou/issue49

refs #49: Refactor DatabaseUtils::to_schema and provide create_tables support for BaseValues