Fetch and return a proper HuntApproval object.

def Get(self):
    """Fetch and return a proper HuntApproval object."""

    args = user_pb2.ApiGetHuntApprovalArgs(
        hunt_id=self.hunt_id,
        approval_id=self.approval_id,
        username=self.username)
    result = self._context.SendRequest("GetHuntApproval", args)
    return HuntApproval(
        data=result, username=self._context.username, context=self._context)