Installs the appstream's appdata file into the correct location and with
the correct name. Fixes the contents to conform to the standard.
Installs a desktop file because it's both required by appstream and by
desktop environments. Note this was currently patched in by
distributions.
Task-number: QTCREATORBUG-17335
Change-Id: If1425ec9fbd0c639550852a8d6e1f15a6b9d77ef
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
