Feature/add online scratch (#157)

* simplify image sample usage

* simplify image

* add scratch demo

* add scipy into dependency

* add demo

* update readme

* add better scratch demo

* add more data

* support mannul image

visualdl/server/visualDL

@@ -84,8 +84,8 @@ mock_data_path = os.path.join(SERVER_DIR, "./mock_data/")
 
 log_reader = LogReader(args.logdir)
 
-graph_image_path = None
-
+# mannully put graph's image on this path also works.
+graph_image_path = os.path.join(args.logdir, 'graph.jpg')
 
 # return data
 # status, msg, data
@@ -203,7 +203,7 @@ def histogram():
 @app.route('/data/plugin/graphs/graph')
 def graph():
     # TODO(ChunweiYan) need to add a config for whether have graph.
-    if graph_image_path is None:
+    if graph_image_path is None or not os.path.isfile(graph_image_path):
         data = {'url': ''}
     else:
         data = {'url': '/graphs/image'}