Rename library/target to KF5::DAV
Summary: Prepares this for the move to Frameworks after 20.04.
Reviewers: KDE PIM, mlaurent
Reviewed By: KDE PIM, mlaurent
Subscribers: mlaurent, cgiboudeaux, kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D26762