update of api docstrings across coach and tutorials [WIP] (#91)

* updating the documentation website
* adding the built docs
* update of api docstrings across coach and tutorials 0-2
* added some missing api documentation
* New Sphinx based documentation

rl_coach/graph_managers/graph_manager.py

@@ -504,6 +504,8 @@ class GraphManager(object):
         :return: None
         """
 
+        self.verify_graph_was_created()
+
         # initialize the network parameters from the global network
         self.sync()