As volunteer manager I want to view and cancel volunteers

Similarly to Program V2, let's separate in Volunteers V2 the view that operates on accepted volunteers from the view that operates on applications/signups.

A list view that displays accepted volunteers as a table. Last name, first name, nick, key dimensions.

A detail view that shows one volunteer. Profile data, dimensions, messages sent to volunteer (table of timestamp and subject; click to open modal showing also message body), shifts (when implemented; out of scope).

On the upper right (admin view actions), a button to cancel the participation of a volunteer (setting the involvement to inactive).