new package: cmst - qt gui for connman

- make network manager in gnome3 as default option, so it can be disabled normally when using `networking.connman.enable = true;`
- new package: graphical (qt) user interface - cmst for managing connman, the most configurable UI I could find at this time
How about using the date of the commit instead of the hash? That way "nix-env -u ..." will be able to handle it properly.