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_submission.rb

@@ -0,0 +1,9 @@
+class SurveySubmission < ActiveRecord::Base
+  belongs_to :user
+  belongs_to :survey
+  has_many :survey_replies, through: :user
+
+  validates :user_id, uniqueness: { scope: :survey_id }
+
+  accepts_nested_attributes_for :survey_replies
+end