add yapf style and apply yapf to format all Python files

This recreates pull request #2192

examples/pybullet/gym/pybullet_envs/deep_mimic/env/env.py

@@ -1,19 +1,21 @@
-from abc import  abstractmethod
+from abc import abstractmethod
 import sys, abc
 if sys.version_info >= (3, 4):
-    ABC = abc.ABC
+  ABC = abc.ABC
 else:
-    ABC = abc.ABCMeta('ABC', (), {})
+  ABC = abc.ABCMeta('ABC', (), {})
 
 import numpy as np
 from enum import Enum
 
+
 class Env(ABC):
-    class Terminate(Enum):
-        Null = 0
-        Fail = 1
-        Succ = 2
-        
-    def __init__(self, args, enable_draw):
-        self.enable_draw = enable_draw
-        return
+
+  class Terminate(Enum):
+    Null = 0
+    Fail = 1
+    Succ = 2
+
+  def __init__(self, args, enable_draw):
+    self.enable_draw = enable_draw
+    return