Namadillo: IBC -> Allow decoding the same asset from multiple chains

[emccorson]

Following on from #1216, there is a bug where if you have the same asset from multiple different chains (e.g. NAM from internal devnet and from housefire), only one will be shown. The problem is that we index the asset balances object by base denom, but this will have multiple entries, so really we should key by base denom + IBC denom trace path. Fix this.