Make ASP-style Confluence hosting feasable

Allow a setup where individual spaces on a Confluence server can be sold as a service.

At a minimum we'll need to:

• Push relevant parts of the global configuration (enabled macros, CamelCase, etc) down to the space-config level
• Allow global admins to enable per-space user management, limiting what groups are available to what spaces, and how many users can be created in these groups.

Virtual hosting would also be useful.