Add support for IBC transfers

[webmaster128]

The message looks like this:

export interface MsgTransfer {
  /** the port on which the packet will be sent */
  sourcePort: string;
  /** the channel by which the packet will be sent */
  sourceChannel: string;
  /** the tokens to be transferred */
  token?: Coin;
  /** the sender address */
  sender: string;
  /** the recipient address on the destination chain */
  receiver: string;
  /**
   * Timeout height relative to the current block height.
   * The timeout is disabled when set to 0.
   */
  timeoutHeight?: Height;
  /**
   * Timeout timestamp in absolute nanoseconds since unix epoch.
   * The timeout is disabled when set to 0.
   */
  timeoutTimestamp: Long;
  /** optional memo */
  memo: string;
}

Some notes here:

• sourcePort should be pre-set to "transfer" by default, but can be changed by the user
• token is required and an aribrary numeric amount and arbitrary string denom (only one, no list here)
• We can use timeoutTimestamp only and put a date in the future. timeoutHeight can be set to undefined. Ideally we offer the user simple options like 12 hours from now, 1 day from now, 2 days from now, 3 days from now, 7 days from now, 10 days from now, 2 weeks from now, 3 weeks from now, 1 month from now, custom time
• The memo in the message is a different memo than the transaction memo. Both can be set individually.