Better design for room URLs

app/views/schedules/_event.html.haml

@@ -17,11 +17,11 @@
     %h4
       - if(event.speakers.any?)
         presented by #{event.speaker_names}
-    - if event.room&.url && @conference.user_registered?(current_user)
-      %p
-        = link_to('Join Event', event.room.url, target: '_blank')
+    %h5
+      = join_event_link(event, current_user)
     %p
       = markdown(truncate(event.abstract, length: 400))
+      -# TODO: More informative text or aria-label.
       = link_to 'more', conference_program_proposal_path(@conference.short_title, event.id) if event.abstract.length > 400
     - if event_schedule.present?
       %span.track