Make organization navigation item conditional

[agjohnson]

Moved from

• Organizations: header navigation link fixes #299

I made an attempt at this and had success, but the additional logic slowed down all views considerably. I used the organizations template filters to try to get a list of user organizations. This might need some more thought, and perhaps we do this in the UX side of things instead of using display time logic -- using the organization selection workflow or something?

This is working for now though, it's just very explicit for most users that only need one organization.

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• When there is only one organization, the menu item should be "Organization" and lead to the detail view for the only org
• When there are more than one organization, go to the listing view
• If the user does not have an organization, perhaps also go to the listing view? This might be the best place to show organization creation onboarding?