a8n/web: Extended campaign list view

Created by: mrnugget

This depends, in parts, on https://github.com/sourcegraph/sourcegraph/issues/7553 and represents the UI portion of extending the campaign list view. See https://github.com/sourcegraph/sourcegraph/issues/7553#issuecomment-577005761 for what needs to be implemented in the UI.

Note that RFC 20 originally specified more work ("An overall campaign list shows all active campaigns (globally, and for a specific namespace) and some indication of their progress"), but that is not necessary yet. Follow the comment linked above.