Big refactoring of registration

- Added datatable gem
- Addaed datatable to events, users (#422), registrations

app/views/conference_registrations/_form.html.haml

@@ -0,0 +1,22 @@
+.row
+  .col-md-12
+    = semantic_form_for(@registration, url: conference_conference_registrations_path(@conference.short_title)) do |f|
+      .tabbable
+        %ul.nav.nav-tabs
+          %li.active
+            = link_to 'Register', '#register-content', 'data-toggle' => 'tab'
+          - if @conference.use_volunteers
+            %li
+              = link_to 'Volunteer', '#volunteer-content', 'data-toggle' => 'tab'
+        .tab-content
+          #register-content.tab-pane.active
+            = render 'conference_registrations/registration', f: f
+          - if @conference.use_volunteers
+            #volunteer-content.tab-pane
+              = render 'conference_registrations/volunteer', f: f
+      - if @conference.user_registered?(current_user)
+        = f.action :submit, button_html: { value: 'Update Registration', class: 'btn btn-primary' }
+        = link_to 'Unregister', conference_conference_registrations_path(@conference.short_title),
+        method: :delete, class: 'btn btn-danger', confirm: 'Are you sure you want to unregister?'
+      - else
+        = f.action :submit, button_html: { value: 'Register', class: 'btn btn-primary', id: 'register' }