print better error warning, in case the physics client/server version mismatch.

fix in b3HashString
remove many unused dependencies from kuka_grasp_block_playback.py (time,math, datetime ,numpy,pylab ,sys, os, fnmatch,argparse were not used!)
move block_grasp_log.bin from Bullet3/data to Bullet3/examples/pybullet/examples/data folder.
PhysicsServerCommandProcessor, derive from CommandProcessorInterface to prepare for different back-end implementation

examples/pybullet/examples/kuka_grasp_block_playback.py

@@ -1,14 +1,6 @@
 import pybullet as p
-import time
-import math
-from datetime import datetime
-from numpy import *
-from pylab import *
 import struct
-import sys
-import os, fnmatch
-import argparse
-from time import sleep
+
 
 def readLogFile(filename, verbose = True):
   f = open(filename, 'rb')