Add type converter

[molcikas]

Add a global and per-field type converter, similar to JPA attribute converters.

Global converters will apply to any field with a given class (or subclass of that class). A per-field converter would apply to a specific field and can override the global converter.

Parameters for a type converter:

• Field Class
• ColumnDataType
• Column serializer (a Converter)
• Field hydrater (a Converter)