Add milestone total weight to the milestone summary

app/views/shared/milestones/_summary.html.haml

@@ -25,8 +25,15 @@
         %span.milestone-stat
           %strong== #{milestone.percent_complete(current_user)}%
           complete
+        - remaining_days = milestone_remaining_days(milestone)
+        - if remaining_days.present?
           %span.milestone-stat
-          %span.remaining-days= milestone_remaining_days(milestone)
+            %span.remaining-days= remaining_days
+        - total_weight = milestone.issues_visible_to_user(current_user).sum(:weight)
+        - unless total_weight.zero?
+          %span.milestone-stat
+            Total weight:
+            %strong= total_weight
 
       .milestone-progress-buttons
         %span.tab-issues-buttons