Allow passing alternate CSS classes to the list item template columns.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/appearance/templates/appearance/generic_list_items_subtemplate.html

@@ -55,7 +55,7 @@
 
             <div class="row">
                 {% for object in object_list %}
-                    <div class="col-xs-12 col-sm-4 col-md-3 col-lg-2">
+                    <div class="{{ column_class|default:'col-xs-12 col-sm-4 col-md-3 col-lg-2' }}">
                         <div class="panel panel-primary panel-item">
                             <div class="panel-heading">