improve readability of schedule table

Align the items in a schedule table to the top of the cell so that
it's more clear which week each deadline is associated with.

http://lists.openstack.org/pipermail/openstack-discuss/2019-October/009862.html

Change-Id: Ib99ba138e9f8cdda0839766c6f810cba90739ecc
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

doc/source/_themes/releases/schedule_table.tmpl

@@ -9,6 +9,7 @@
 .. list-table::
    :header-rows: 1
    :widths: 15 5 30 30
+   :class: schedule
 
    - * Week
      * 

doc/source/_themes/releases/static/css/styles.css

@@ -44,6 +44,13 @@ ol.loweralpha {
     font-weight: 400;
 }
 
+/* ensure the entries in the schedule table align so it is easy to
+   read when multiple deadlines fall on the same week (see
+   schedule_table.tmpl) */
+table.schedule td {
+    vertical-align: top
+}
+
 /* lists within tables don't need as much margin */
 td ul {
 	margin-bottom: 0;