Calculate hours when only one day is left.

This {% widthratio %} trick is something I found online that didn't
require a django-math module to work, but I would have rather written
something that:

  (b) Could have a different message when there is only one hour
      left: “less than one hour left” (i.e., tested if hours == 1)

  (c) Will say “hour” instead of “hours” when there is exactly 1 hour
      left.

conservancy/fundgoal/templates/fundgoal/fundraiser_goal_banner_partial.html

@@ -36,7 +36,7 @@
           {% if sitefundgoal_timeleft.total_seconds <= 0 %}
             The
           {% elif sitefundgoal_timeleft.days == 0 %}
-            Through today only, the
+            For the next {% widthratio sitefundgoal_timeleft.total_seconds 3600 1 %} hours <strong>only</strong>, the
           {% elif sitefundgoal_timeleft.days == 1 %}
             Through tomorrow only, the
           {% elif sitefundgoal_timeleft.days < 14 %}