cache some settings

we can SIGHUP if we ever change them

Change-Id: I0e7d0fa63ce0e368e890eb7ea8d5e657fa3820a1
Reviewed-on: https://gerrit.instructure.com/23729
Reviewed-by: Zach Wily <zach@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Tested-by: Cody Cutrer <cody@instructure.com>

app/models/account.rb

@@ -232,15 +232,15 @@ class Account < ActiveRecord::Base
   end
 
   def terms_of_use_url
-    Setting.get('terms_of_use_url', 'http://www.instructure.com/policies/terms-of-use')
+    Setting.get_cached('terms_of_use_url', 'http://www.instructure.com/policies/terms-of-use')
   end
 
   def privacy_policy_url
-    Setting.get('privacy_policy_url', 'http://www.instructure.com/policies/privacy-policy-instructure')
+    Setting.get_cached('privacy_policy_url', 'http://www.instructure.com/policies/privacy-policy-instructure')
   end
 
   def terms_required?
-    Setting.get('terms_required', 'true') == 'true'
+    Setting.get_cached('terms_required', 'true') == 'true'
   end
 
   def require_acceptance_of_terms?(user)

app/models/content_participation_count.rb

@@ -117,7 +117,7 @@ class ContentParticipationCount < ActiveRecord::Base
   # - unmuting an assignment with submissions
   # - deleting a discussion/announcement/assignment/submission
   def ttl
-    Setting.get('content_participation_count_ttl', 30.minutes).to_i
+    Setting.get_cached('content_participation_count_ttl', 30.minutes).to_i
   end
   private :ttl
 end

app/presenters/grade_summary_presenter.rb

@@ -172,7 +172,7 @@ class GradeSummaryPresenter
   protected
 
   def allow_loading_all_submissions?
-    threshold = Setting.get('grade_distributions_submission_count_threshold', '0').to_i
+    threshold = Setting.get_cached('grade_distributions_submission_count_threshold', '0').to_i
     @context.allows_gradebook_uploads? && (threshold == 0 || @context.submissions.count < threshold)
   end
 end