Update to wasmvm / cosmwasm 0.16

[ethanfrey]

There will be one more update before

Key Changes:

• Lots of changes to the IbcChannel*Msg types
• CounterPartyVersion is no longer in IbcChannel but in some of those messages
• Change standard contract_address event attribute (for wasm type) to _contract_address.
• Enforce the contract cannot return any _* attributes and thus conflict with any special "trusted" attributes from the runtime.
• Handle custom events from IbcBasicResponse and IbcReceiveResponse (not just attributes)

[webmaster128]

contract_address event attribute (for wasm type) to _contract_address.

This affects custom events as well. Alex started injecting wasmd attributes into those as well to make it possible to trust the origin of those events (see contractSDKEventAttributes in #548). This makes reserving all _* more important and powerful. You then get the guarantee that all _* attributes are written by wasmd, not the contract.