Add surveys; custom generated by admins

Available during registration or after conference

Co-authored-by: Shyukri <shshyukriev@suse.com>
Co-authored-by: Henne <hvogel@opensuse.org>
Co-authored-by: Moises <mdeniz@suse.com>

app/models/survey.rb

@@ -0,0 +1,13 @@
+class Survey < ActiveRecord::Base
+  belongs_to :surveyable, polymorphic: true
+  has_many :survey_questions
+  has_many :survey_submissions
+
+  enum target: [:after_conference, :during_registration]
+  validates :title, presence: true
+
+  def active?
+    now = Time.now.in_time_zone(surveyable.timezone)
+    now >= start_date && now <= end_date
+  end
+end