Hints for qalculate-gtk in main

Warnings

• asv-cid-desktopapp-is-not-rdns
  qalculate-gtk.appdata.xml:3 - qalculate-gtk.desktop
  The component ID is not a reverse domain-name. Please update the ID to avoid future issues and be compatible with all AppStream implementations. You may also consider to update the name of the accompanying .desktop file to follow the latest version of the Desktop-Entry specification and use a rDNS name for it as well. In any case, do not forget to mention the new desktop-entry in a <launchable/> tag for this component to keep the application launchable from software centers and the .desktop file data associated with the metainfo data.