Improve UX of orga onboarding (creating a group)

[loicknuchel]

Group management have already a lot of options and a lot more will come so users wanting to create a new group can be a bit lost.
We should improve this so people can easily create groups and start using gospeak.

Here are some ideas:

• hide some menu/features at the beginning, they should be enabled in settings when needed (such as sponsors or cfps)
• have better empty states (group dashboard essentially) that suggest basic actions to create the first elements (events or integrations essentially)
• add meaningful messages, tooltips and helper texts to understand what has been done, what to do and what could be done next
• add "quick form" actions to change things in the meaningful places (instead of always using the "edit" page)
• add a helper page explaining how gospeak works, the basic concepts and actions that can be performed
• define a richer default conf so there is less things to do to get started