don't allow course section end date to be before start date

test plan:
* shouldn't be able to edit a course section to make
 the end date before the start date

closes #CNVS-34979

Change-Id: I5712fce42de1084ba19f4e71043f7ef61d4dd4ba
Reviewed-on: https://gerrit.instructure.com/103595
Tested-by: Jenkins
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>

app/models/course_section.rb

@@ -39,6 +39,7 @@ class CourseSection < ActiveRecord::Base
   validates_presence_of :course_id, :root_account_id, :workflow_state
   validates_length_of :sis_source_id, :maximum => maximum_string_length, :allow_nil => true, :allow_blank => false
   validates_length_of :name, :maximum => maximum_string_length, :allow_nil => false, :allow_blank => false
+  validate :validate_section_dates
 
   has_many :sis_post_grades_statuses
 
@@ -50,6 +51,15 @@ class CourseSection < ActiveRecord::Base
   include StickySisFields
   are_sis_sticky :course_id, :name, :start_at, :end_at, :restrict_enrollments_to_section_dates
 
+  def validate_section_dates
+    if start_at.present? && end_at.present? && end_at < start_at
+      self.errors.add(:end_at, t("End date cannot be before start date"))
+      false
+    else
+      true
+    end
+  end
+
   def maybe_touch_all_enrollments
     self.touch_all_enrollments if self.start_at_changed? || self.end_at_changed? || self.restrict_enrollments_to_section_dates_changed? || self.course_id_changed?
   end

public/javascripts/section.js

@@ -48,7 +48,6 @@ define([
       error: function(data) {
         $edit_section_form.loadingImage('remove');
         $edit_section_form.show();
-        $edit_section_form.formErrors(data);
       }
     })
     .find(":text")