Added mining related RPC method stubs
Added mining related RPC method stubs

ethereum/pyethapp,changwu-tw/pyethapp,RomanZacharia/pyethapp,danielnovy/test,ethereum/pyethapp,gsalgado/pyethapp,heikoheiko/pyethapp,changwu-tw/pyethapp,kustomzone/pyethapp,gsalgado/pyethapp,RomanZacharia/pyethapp,vaporry/pyethapp,d-das/pyethapp