alpha release of crabclient library api

fix #4091 

Introducing the client library API. 

Example of command: 

from CRABClient.ClientAPI.Command import Command 

cmd = Command()
submitdict = cmd('submit', '--wait', config=<crabconfig.py string>)
statusdict = cmd('status', '--long', task=<task name string>)
checkwritedict = cmd('checkwrite', site='T2_CH_CERN')

each command will return a dict, must write an option that do not take variable before (--wait, --long, --summary, etc), option that take argument (--config, --task, --sort, --instance, etc). 

document draft: https://twiki.cern.ch/twiki/bin/viewauth/CMS/CRABClientLibraryAPI

please ignore the ClientLogger libraray for the moment