Milo: Add timestamp name and tooltip

milo/appengine/frontend/static/buildbot/css/default.css

 /* Copyright 2015 The LUCI Authors. All rights reserved.
  * Use of this source code is governed under the Apache License, Version 2.0
  * that can be found in the LICENSE file.
  */
 
 body.interface {
   margin-left: 30px;
   margin-right: 30px;
   margin-top: 20px;
   margin-bottom: 50px;
@@ skipping 603 matching lines @@
 }
 
 .file {
   font-weight: bold;
 }
 
 .result {
   padding: 0.3em 1em 0.3em 1em;
 }
 
+.ui-tooltip {
+    white-space: pre-line;
+    font-size: medium;
+}
+
 /* log view */
 .log * {
   vlink: #800080;
   font-family: "Courier New", courier, monotype, monospace;
   font-size: 1.5em;
 }
 
 span.stdout {
   color: black;
 }
@@ skipping 76 matching lines @@
   display: inline;
 }
 
 div.step-text:first-child {
     display: inline;
 }
 
 .hide .verbosity-Hidden {
   display: none;
 }