allow excluding students from global surveys

also bump switchman to allow for .uniq across shards

fixes CNVS-14873

test plan
 - site admin survey should go to students by
   default
 - accounts/self/settings should have checkbox to
   include students in global surveys checked by
   default
 - accounts that have unchecked setting should
   exclude students from global surveys
 - regular announcements should still get to
   students
 - checkbox should only be visible to site admin

Change-Id: I5b268f3e19f8710cdaf0e40f37e9af87ff437649
Reviewed-on: https://gerrit.instructure.com/44457
QA-Review: August Thornton <august@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>