Add Dockerfiles for testing utopic and Debian unstable

For some reason Ctrl+Shift+I/Ctrl+Shift+D do not work in the debian
image, but I can get the Gtk+ inspector with GTK_DEBUG=interactive
/app/memgraphinator.py.

In the Debian image there's some weirdness probably because of missing
gsettings defaults, e.g. titlebar has minimize and maximize buttons.
Also the shadows look bad -- bug or misconfiguration?