Purpose: Conversion interface to allow conversion between object and data types.
This can be used in any mapping to convert between the object and data types without requiring code
placed in the object model.
TopLink provides several common converters, but the application can also define it own.
If the converter converts the value to a mutable value, i.e.
a value that can have its' parts changed without being replaced,
then it must return true. If the value is not mutable, cannot be changed without
replacing the whole value then false must be returned.
This is used within the UnitOfWork to determine how to clone.