Changes UserData to use global identifiers and makes linkIndex optional.

This removes the need to specify the body id/link index when retrieving a user data entry.
Additionally, user data can now optionally be set to visual shapes as well.

The following public pybullet APIs have changed (backwards incompatible)
addUserData and getUserDataId
  Makes linkIndex parameter optional (default value is -1)
  Adds optional visualShapeIndex parameter (default value is -1)

getUserData and removeUserData
  Removes required parameters bodyUniqueId and linkIndex

getNumUserData
  Removes required bodyUniqueId parameter

getUserDataInfo
  Removes required linkIndex parameter
  Changes returned tuple from (userDataId, key) to (userDataId, key, bodyUniqueId, linkIndex, visualShapeIndex)

examples/SharedMemory/SharedMemoryPublic.h

@@ -274,6 +274,7 @@ struct b3JointInfo
 
 
 enum UserDataValueType {
+  USER_DATA_VALUE_TYPE_NOT_USET = -1,
 	// Data represents generic byte array.
 	USER_DATA_VALUE_TYPE_BYTES = 0,
 	// Data represents C-string
@@ -287,13 +288,6 @@ struct b3UserDataValue
 	char* m_data1;
 };
 
-struct b3UserDataGlobalIdentifier 
-{
-	int m_bodyUniqueId;
-	int m_linkIndex;
-	int m_userDataId;
-};
-
 struct b3UserConstraint
 {
     int m_parentBodyIndex;