Revised navigation: org selection behavior

Provide the user with the ability to switch organizations when they have access to more than one. This issue is partially blocked by UI work, but backend logic can be worked on in advance.

Implementing this design will require us to make a decision about how / where to store the currently selected organization (local storage? url? location in the app?).

We will also have to consider what happens after an organization is selected. Will the user be sent to the organization's main page?

• Partially blocked by #409
• Partially blocked by #408

Acceptance Criteria

• User can see their currently selected organization
• User can switch to another organization