A nicer look for the documents listing

This change includes a filthy hack around how Django handles
change_list_results.html -- I'm not thrilled with it, but it's as
elegant as I could come up with.  I'm happy to field alternative ideas.
More details can be found in `documents/templatetags/hacks.py`

Specifically, this merge includes a significant facelift to the
documents listing page, moving away from the tabular layout and toward a
tileset look.  I tried fiddling with the colours, but I just don't have
any skills in that area, so we're all stuck with Django'd default
colours until someone with an eye for colour can submit a better CSS.

src/documents/admin.py

@@ -58,7 +58,7 @@ class DocumentAdmin(CommonAdmin):
         }
 
     search_fields = ("correspondent__name", "title", "content")
-    list_display = ("created", "title", "thumbnail", "correspondent", "tags_")
+    list_display = ("title", "created", "thumbnail", "correspondent", "tags_")
     list_filter = ("tags", "correspondent", MonthListFilter)
     ordering = ["-created", "correspondent"]