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/views/surveys/_list.html.haml

@@ -0,0 +1,7 @@
+- surveys.each do |survey|
+  - if survey.survey_submissions.find_by(user: current_user)
+    %i.fa.fa-check-square-o.text-success{ title: 'Thank you for filling out the survey' }
+  - else
+    %i.fa.fa-minus-square-o.text-danger{ title: 'Please fill out the survey' }
+  = link_to survey.title, conference_survey_path(conference.short_title, survey)
+  %br