Add demo in init

Author: b-yogesh

chartlets.py/demo/my_extension/__init__.py

@@ -2,8 +2,10 @@
 from .my_panel_1 import panel as my_panel_1
 from .my_panel_2 import panel as my_panel_2
 from .my_panel_3 import panel as my_panel_3
+from .my_panel_4 import panel as my_panel_4
 
 ext = Extension(__name__)
 ext.add(my_panel_1)
 ext.add(my_panel_2)
 ext.add(my_panel_3)
+ext.add(my_panel_4)