viewer: store appstream file in metainfo dir (#296)
viewer: store appstream file in metainfo dir (#296)

"appdata" is the legacy path for AppStream files, and now such directory should be called "metainfo".

https://www.freedesktop.org/software/appstream/docs/chap-Quickstart.html#sect-Quickstart-DesktopApps
AravisProject/aravis,AravisProject/aravis,AravisProject/aravis,AravisProject/aravis,AravisProject/aravis