Add more options for surveys

* Survey period constraints
* Add abilities
* Enforce required questions
* Update survey_submssion updated_at
* Do a full match of possible answer and user reply

app/models/survey.rb

@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 class Survey < ActiveRecord::Base
   belongs_to :surveyable, polymorphic: true
-  has_many :survey_questions
-  has_many :survey_submissions
+  has_many :survey_questions, dependent: :destroy
+  has_many :survey_submissions, dependent: :destroy
 
   enum target: [:after_conference, :during_registration]
   validates :title, presence: true
 
   def active?
+    return false unless start_date && end_date
     now = Time.now.in_time_zone(surveyable.timezone)
     now >= start_date && now <= end_date
   end