NCO: Add IMAddress and adapt existing IM classes and properties

This commit applies various changes to the ontology for multiple
reasons. It increases consistency between email addresses, phone
numbers, and IM addresses. This enables the use of anonymous contacts
for IM messages. Furthermore, this commit also simplifies queries
that involve merged contacts, which improves the performance
significantly. Despite all the changes, full backward compatibility is
retained during a transition period as this commit does not yet remove
the deprecated classes and properties.

The class nco:IMAddress and the property nco:hasIMAddress have been
added. nco:hasIMAddress can be used by any nco:Contact and represents
an instant messaging address consisting of nco:imID and nco:imProtocol.
This improves consistency with how email addresses and phone numbers
are handled in NCO.

nco:IMContact has been deprecated in favor of using nco:PersonContact
with nco:hasIMAddress. This avoids special casing IM contacts.

The address of a nco:IMAccount is now stored in nco:imAccountAddress,
this allows to consolidate the nearly duplicate properties such as
nco:imId and nco:imContactId and the other nco:im* and nco:imContact*
property pairs. To improve consistency among these properties and ease
transition, nco:imContactCapability has been renamed to
nco:imCapability.

nco:hasIMAccount has been deprecated as it did not provide any
information as it was only applicable to a single subject,
nco:default-contact-me.

nco:fromIMAccount has been deprecated and replaced by nco:hasIMContact,
which provides the same information in reversed form, that is, it links
IM accounts of the user to IM contacts (buddy list).

nco:MetaContact and nco:metaContact have been deprecated in favor of
storing merged contacts. Contact details can be linked to the data
source with named graphs in future versions of Tracker. This provides
vastly simpler and more efficient access to merged contacts.