All users and organizations to have accounts

[techsmyth]

Description

As a developer I want to have a simpler domain model

Acceptance criteria

• [ ] All new users and organizations to have an account created
• [ ] All existing users and organizations that are not a host of an account to have an account created that they are hosting
• [ ] Space creation mutation updated to specify creating a space on an account
• [ ] Remove allowing an account to have a different host; that is set on account creation and cannot be modified thereafter.

Note: currently still only one allowed.

Additional Context