Updated the design of milestone list status

app/views/shared/_milestone_expired.html.haml

-- if milestone.expired? and not milestone.closed?
-  %span.cred (Expired)
-- if milestone.upcoming?
-  %span.clgray (Upcoming)
 - if milestone.due_date || milestone.start_date
-  %span
+  %div
     = milestone_date_range(milestone)
+- if milestone.expired? and not milestone.closed?
+  .status-box.status-box-expired Expired
+- if milestone.upcoming?
+  .status-box.status-box-mr-merged Upcoming
+- if milestone.closed?
+  .status-box.status-box-closed Closed