Onboarding: Better flow if signup without invite

[Jaymassena]

When user tries the app by direct signup then improve the flow:

• Add step to invite to their default channel.
• Leave them in their default channel with a call to action:
• Action: Post your first message.
• Action: Personalize your channel.

[Jaymassena]

Fixed. We now leave them in their default channel with a popup message and a call to action.