list events from predecessor series

if the predecessor series id set at the series form, the list of events
includes the predecessor dates. This can help to get an overview, if the
series moved to another project or studio, or editors change continue
their work in another series.

website/agenda/planung/css/calendar.css

@@ -528,4 +528,12 @@ div.play .error {
     margin: 1px;
     border-radius: 4px;
     text-align: center;
-}
+}
+
+#content tr.event.predecessor{
+    #background:#f0cccc;
+    opacity:0.5;
+}
+#content tr.event.predecessor:hover{
+    #background:#fdcccc
+}