D21381: use org.freedesktop.appstream-glib package to validate appstream data

[Nathaniel Graham]

ngraham added a reviewer: apol.

REPOSITORY
  R240 Extra CMake Modules

REVISION DETAIL
  https://phabricator.kde.org/D21381

To: mgallien, aacid, yurchor, apol
Cc: kde-frameworks-devel, kde-buildsystem, bencreasy, michaelh, ngraham, bruns