Add modern conference show page with admin toggle

Introduces a new conference splash page design (show_new) with a modern
layout. Admins can enable it per conference from the splashpage settings.

Author: davidsf

app/assets/stylesheets/application.css

@@ -7,6 +7,7 @@
  *= require moraga-schedule-print
  *= require moraga-dashboard
  *= require moraga-splash
+ *= require moraga-splash-new
  *= require moraga-fonts
  *= require bootstrap-markdown
  *= require bootstrap-datetimepicker