Make it clear when user reaches end of events timeline

Before there was no padding at the bottom, so a user would think
they could still scroll, when they could scroll no more. This adds
a horizontal rule to the end of the events timeline, so the user knows
that they have reached the end.

Change-Id: Icbc148a7c257067c804055fbb0a6aa7c89e33681

src/app/stories/template/detail.html

@@ -292,6 +292,7 @@
                     </button>
                 </div>
             </form>
+            <hr />
         </div>
     </div>
 </script>