Packaging Metadata

Based on the following commits

commit 023f2dc386164ed5bfd43a26fd65433ab2f49cca
Author: Igor Gnatenko <i.gnatenko.brain@gmail.com>
Date:   Wed Nov 19 11:00:34 2014 +0300

    implement appdata to show laby in Software Centers

    Reference: https://github.com/sgimenez/laby/issues/31
    Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

commit cae6ecc53f777940dbe5f4dd4b3cde992241a9b3
Author: Igor Gnatenko <i.gnatenko.brain@gmail.com>
Date:   Wed Nov 19 10:53:41 2014 +0300

    improve desktop-file

    Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>