DATAMONGO-1001 - Fix saving lazy loaded object.

We now resolve the target type for Cglib proxied objects and initialize lazy loaded ones before saving.

As it turns out CustomConversions already knows how to deal with proxies correctly. Therefore we added an explicit test to assert that.
DATAMONGO-1001 - Fix saving lazy loaded object.

Renamed `LazyLoadingProxy.initialize()` to `getTarget()`.

Should only be applied to 1.6.