Automatically create a show-off distribution / group

[almet]

So people can test the tool without having to create too much things. This could be easier once #32 is implemented so we can directly import a few files.

[almet]

One way to solve this would be to :

1. Detect that the software was just installed, and if so propose to go in "demo" mode.
2. Once the demo mode is "on", provide a way to wipe-out all of these "demo" data, and start from a blank state.

The demo mode could have a nice ribbon on the top, so people don't mistake this from an actual delivery.

[almet]

Fixed in b60a9ab