Performance improvements to server-side admin framework.

The strongly typed server-side APIs now retrieve and cache their property values during construction so that subsequent calls to property getters no longer have to repeatedly access the underlying ServerManagedObject. This avoids having to repeatedly perform hash-table look-ups in the ServerManagedObject and, in the case of single-valued properties, temporary construction of iterators.

I have also modified the ServerManagedObject#getPropertyValues() method to return an UnmodifiableSortedSet rather than a defensive copy and updated the javadoc in the generated server-side getters to reflect that the returned set is unmodifiable.