Add a new type of transaction to support OTC

[whitefen]

Add a new message like this

type MsgSupervisedSend struct {
    FromAddress sdk.AccAddress `json:"from_address"`
    Supervisor  sdk.AccAddress `json:"supervisor"` // ！！！
    ToAddress   sdk.AccAddress `json:"to_address"`
    Amount      sdk.Coin      `json:"amount"`
    UnlockTime  int64          `json:"unlock_time"`
    Reward      int64          `json:"reward"`
    Operation   byte   `json:"operation"`
}