Add HD Wallet integration (temporary and hacky!!!)

Add RPC/Websocket calls for:

getdepositscript
createseries
replaceseries
thawseries
This duplicates some code from LoadVotingPool(). It should be possible to do something like this in CreateSeries (which would allow us to get rid of ExistsVotingPool altogether):
  pool, err := LoadVotingPool(...)
  if err == ErrVotingPoolNotExists {
    pool, err := w.Manager.CreateVotingPool(poolID)
    // check error
  }
  CreateSeries(...)