add facebook login function

add facebook for python
add login.py  url is /login
add login.html  and use facebook JSSDK
add basehandler.py  to set tornado self.current_user
add tool/memcache.py
change tool/datastore  ,add class User Image
change main.py  now if you login will see 'Hello , YOUR_NAME',add a path /login
add tool/config.py  to get secret strings
add tool/facebook/requests/ for facebook tool ,version is 2.1.0,the latest one have some problem
add tool/users.py  to set up the user or fbuser