Events should offer Spaces as the view policy options
Summary: Ref T8687, Events should offer Spaces as the view policy options
Test Plan: Create event, choose default Space, save, edit, choose different Space, save, new policy should be reflected on Event.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T8687
Differential Revision: https://secure.phabricator.com/D13459