App/cell lifecycle 1: installing/uninstalling

[pdaoust]

• Front-end code samples for calling API endpoints
• Installation of an app
• Uninstalling an app
• How roles are filled based on provisioning strategy [EDIT: covered by #517]
• Cell statuses

Broken out from #479.

[pdaoust]

Marked as awaiting stakeholder pull becuase so far we're catering to hApp devs, not devs building a runtime.