Resolve "Run full register printout generation in background"

Closes #229 (closed)

aleksis/apps/alsijil/templates/alsijil/print/full_register.html

@@ -17,8 +17,8 @@
     <h5>{{ school_term }}</h5>
     <p>({{ school_term.date_start }}–{{ school_term.date_end }})</p>
     {% static "img/aleksis-banner.svg" as aleksis_banner %}
-    <img src="{% firstof request.site.preferences.theme__logo.url aleksis_banner %}"
-         alt="{{ request.site.preferences.general__title }} – Logo" class="max-size-600 center">
+    <img src="{% firstof SITE_PREFERENCES.theme__logo.url aleksis_banner %}"
+         alt="{{ SITE_PREFERENCES.general__title }} – Logo" class="max-size-600 center">
     <h4 id="group-desc">
       {{ group.name }}
     </h4>