wizard: improve setup wizard

- Reduced overall size of the dialog
- Changed join the ring button to next
- Change style of the next button
- Allow user to create an account with 'Unknown' name
- Add a share button on main screen :
    This allow only to send the ringID in text form
    by mail, a real share callback to the system is
    impossible without being a native app.

Change-Id: I37235cd798b22ac4dd57b42b939f9e9541237dd6
Tuleap: #366