This commit improves the SeasideImport API by allowing clients to
specify their own SeasideContactBuilder implementation when
converting the list of Versit documents into storage QContacts.

The SeasideContactBuilder allows the client to parametrise things
like the contact filter used to determine the subset of mergable
contacts, the merge strategy to use, and so on.

When merging imported contacts into the existing data set, ensure that
contacts with 'bluetooth' syncTarget values are considered as potential
merge candidates.

QContactFamily and QContactGeoLocation types are now supported by the
qtcontacts-sqlite backend.

Contacts with 'bluetooth' or 'was_local' sync target values should
preserve these properties during export/import.

Some detail types cannot be supported by the qtcontacts-sqlite
backend; remove them from contacts before attempting to import.

UIDs found in VCF are not very reliable; if a UID match is found where
the contacts have name details that do not match, ignore the UID match
and remove the Guid detail from one contact.

When a vCard record does not contain valid name information, ensure
that is nickname is present.  This allows us to be certain that each
contact has either a valid name or a nickname.

Although they won't work correctly, allow IM accounts to be imported.

This practice is possibly affected by iterator invalidation in some
way I can't locate.  In any case, index-based operations are not
going to make any performance difference.

Remove obsolete contacts only after traversing indexed contact list.

Should be used by the batch importer and the GUI importer.