roster: show activity columns based on "usage reports" permissions

fixes CNVS-13436

test plan:
  * for teachers, disable these permissions:
    * Add/remove other teachers, course designers or TAs to the course
    * Add/remove students for the course
  * enable View usage reports for the course
  * log in as a teacher
  * view the course roster
  * confirm that the activity columns are visible

Change-Id: Ida208431c5d94b5f6f3a7a2df2901e5c4300b3a0
Reviewed-on: https://gerrit.instructure.com/35891
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Anthus Williams <awilliams@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>

app/controllers/context_controller.rb

@@ -200,7 +200,8 @@ class ContextController < ApplicationController
         :permissions => {
           :manage_students => (manage_students = @context.grants_right?(@current_user, session, :manage_students)),
           :manage_admin_users => (manage_admins = @context.grants_right?(@current_user, session, :manage_admin_users)),
-          :add_users => manage_students || manage_admins
+          :add_users => manage_students || manage_admins,
+          :read_reports => @context.grants_right?(@current_user, session, :read_reports)
         },
         :course => {
           :id => @context.id,

app/views/jst/courses/roster/rosterUser.handlebars

@@ -22,7 +22,7 @@
   <div>{{enrollmentName role}}</div>
   {{/each}}
 </td>
-{{#if canViewLoginIdColumn}}
+{{#if ENV.permissions.read_reports}}
 <td>
   {{#each enrollments}}
     <div {{contextSensitiveDatetimeTitle last_activity_at }}>

app/views/jst/courses/roster/rosterUsers.handlebars

@@ -10,7 +10,7 @@
       {{/if}}
       <th>{{#t "section"}}Section{{/t}}</th>
       <th>{{#t "role"}}Role{{/t}}</th>
-      {{#if canViewLoginIdColumn}}
+      {{#if ENV.permissions.read_reports}}
       <th>{{#t "last_activity"}}Last Activity{{/t}}</th>
       <th>{{#t "total_activity"}}Total Activity{{/t}}</th>
       {{/if}}