Bump the required TelepathyQt version to 0.9.8 and use the new targets

TelepathyQt 0.9.8 exports TelepathyQt5::Core and TelepathyQt5::Service instead
of the old 'telepathy-qt5' target.

Use the new targets to fix possible linking issues.

Reviewed By: arojas, tcberner, heikobecker

Differential Revision: https://phabricator.kde.org/D26750