fix(timeline): #778 Tooltip does not work with background items in timeline (#2703)

* Fix redraw order
* Fix error when option is not defined
* Allow template labels
* Add .travis.yml file
* Add experiment travis code
* Fix react example
* Make items z-index default to 1

lib/timeline/component/css/item.css

@@ -6,6 +6,7 @@
   border-width: 1px;
   background-color: #D5DDF6;
   display: inline-block;
+  z-index: 1;
   /*overflow: hidden;*/
 }