This patch allows to add a 'groups' statement to each part, define one or more groups for each one, and use the groups for dependency management. This way, it is possible to add all the binaries and libraries parts to a "binaries" group, and make another part deppend on that group (just using the 'after' statement like with a part name). This is mainly useful in big snapcraft.yaml files with a lot of parts, like the gnome-XX-sdk ones. This MR replaces https://github.com/snapcore/snapcraft/pull/3823 - [x] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? -----