MsgTransfer memo support

[webmaster128]

There is currently various sort of trouble around support for the memo field in MsgTransfer. This meta issue should provide an overview.

Protobuf support

The Telesope-generated proto types support the memo field for a long time. cosmjs-types 0.7.0 has it and earlier versions don't.

Amino JSON support

The MsgTransfer can be signed using sign mode direct. However, Amino JSON signing support was lacking for some time.

• toAmino: Added in Add memo field to AminoMsgTransfer #1456/Add memo field to AminoMsgTransfer #1477 and sipped as part of 0.31.2
• fromAmino: Added in 9d5aece and sipped as part of 0.31.3

SigningStargateClient.sendIbcTokens

This was brought up in #1413. Right now the memo argument in sendIbcTokens belongs to the transaction, not MsgTransfer. Designing an API with two different memos is a mess. Given that CosmJS will move away from opinionated methods like sendIbcTokens it is more sustainable if users compose their messages manually and then use signAndBroadcast with an MsgTransferEncodeObject input. The methods on SigningStargateClient will die eventually. So this part is a wontfix.

Edit: #1504 deprecates SigningStargateClient.sendIbcTokens