Add Snap packaging

Please consider allowing the Snap packaging to be included in your repository.

I have recently packaged GNOME 2048 as a Snap. It is not yet published in the Snap Store (it needs manual review because of the D-Bus interface that all GtkApplication apps use so that may take a few days.)

If you accept the Snap packaging, the Ubuntu Desktop team can easily automate nightly builds from the stable and master branches. Snap includes multiple channels. Nightly builds from the master branch can go to the edge channel and builds from the stable branch can go to the candidate channel so they can be verified to work before being manually pushed to the stable channel.

By the way, the Snap sandbox didn't like the org.gnome.2048 D-Bus name so I'm glad you recently changed it! That means that 3.31 will be the first version that we can make available on Snap. I think this blocked making the game available earlier on Snap.

If you have any issues with the Snap packaging, please contact the Ubuntu Desktop team. If you're interesting in helping maintain the Snap version, please let us know too.