Project: improve detail page when organizations are enabled

[stsewd]

Current page looks like this

What's missing?

• Link to the organization
• Maintainers is listing owners only (it's using project.users instead of listing the members using our querysets)

[agjohnson]

The link is easy to add, the label in the top right of the project header just needs to link to the organization detail view.

Maintainer listing is duplicate of:

• https://github.com/readthedocs/ext-theme/issues/137
• And somewhat https://github.com/readthedocs/ext-theme/issues/234