Support embeddable object with 1-N (non-relation) field with join table

[andyjefferson]

If we have an embedded object and that object has a 1-N field (either relation, or Collection of some basic type) this implies having a join table for the related object(s). The join table needs a FK back to the owner, but in this case the owner object has no such 'id' and would have to navigate back to the owner that it is embedded in. This is not currently fully supported, but we could one day. See also http://www.datanucleus.org/servlet/jira/browse/NUCRDBMS-989

Need to consider the following situation also.

@PersistenceCapable
@table(name="TABLE_A")
class A
{
@PrimaryKey
long id;

@Embedded
B b;

}

@PersistenceCapable
class B
{
String name;

@JoinTable(name="TABLE_B_VALUES")
Set<String> values;

}

If class B is "embeddedOnly" then we will have TABLE_A and TABLE_B_VALUES.
If class B is not "embeddedOnly" then we will have TABLE_A, TABLE_B, TABLE_B_VALUES and the owner mapping of TABLE_B_VALUES will be confused because it needs datastore-id when used from owner B, and application-id (long) when used from owner A (with B embedded into A).

[andyjefferson]

Still needs tests adding, and either cater for multiple points of embedding, or raise separate issue for that

[andyjefferson]

See #139 for the ability to embed in multiple owners.