BCQ variant on top of DDQN (#276)

* kNN based model for predicting which actions to drop
* fix for seeds with batch rl

rl_coach/coach.py

@@ -259,7 +259,7 @@ class CoachLauncher(object):
                 graph_manager.env_params.level = args.level
 
         # set the seed for the environment
-        if args.seed is not None:
+        if args.seed is not None and graph_manager.env_params is not None:
             graph_manager.env_params.seed = args.seed
 
         # visualization