Show prices for logged in users

Trip prices are visible on trip list, accommodation list,
conference list and travel list.

Prices are hidden if not logged in, except conference prices.

Still need to show prices on individual trip page.

templates/conference_list.html

@@ -5,7 +5,7 @@
 {% block title %}Conferences - Edward Betts{% endblock %}
 
 {% block style %}
-{% set column_count = 8 %}
+{% set column_count = 9 %}
 <style>
 .grid-container {
   display: grid;