[RIM Issue] Exetnsibility of PostalAddress

* Goran: PostalAddress, EmailAddress need id because of Slots
         o Farrukh: This is a bug. We have two options:
               + a) Could make them derive from Identifiable and remove
                 the Slots within their definition since that would be
                 inherited.
               + b) Not make them extensible and remove slots from
                 these types
         o Resolution: Do (a) for PostalAddress and (b) for others
           because PostalAddress has known use cases for requiring
           extensibility.

Upon reflection it seems better to leave PostalAddress to be 
not-extensible via Slots (same as EmailAddress, TelephoneNumber etc.) 
for the following reasons:

-This would create a special case (one of) which is always a 
questionable thing

-We have been doing OK without this ability so far and no one has raised 
an issue

-PostalAddress can be extended via Slots on the Composite class (e.g. 
Organization) where the the name URN of SLot can indicate which 
attribute it is extending: 
urn:my:org:Organization.PostalAddress.home.someExtensionAttributeOfPostalAddress

-We are short on time and this change would require some careful thought 
because it is a new situation.

-PostalAddress extensibility can be deferred to version 4

Please let me know if you have any strong objections to simply taking 
the Slot sttributes out of PostalAddress class for version 3 (not 
extensible). Thanks.

-- 
Regards,
Farrukh