[libcontacts] Improve handling of imports without names

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.
[libcontacts] Add test for SeasideImport
[libcontacts] Skip UID matches where name details differ

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.
Merge pull request #71 from matthewvogt/empty-name-import

[libcontacts] Improve handling of imports without names