Cosmos-sdk: Multiple Msgs in a Tx

[sunnya97]

A tx should be able to have multiple msgs, not just a single one. Inherited from #669

[rigelrozanski]

I'd propose this is post launch unless it's a trivial implementation, or somehow critical to the hub... I don't see how it is

[cwgoes]

@sunnya97 Do you think this needs to be done pre-launch?

[zmanian]

I vote post-launch

[AdityaSripal]

Closed in #1266