Add support for saving debugging messages, generic queriers

[ouiliame]

We add a new property debugMsgs: string[] to VMInstance, to which contract calls to deps.api.debug(...) will append. Previously, we simply printed the string out to console (which matches the behavior of cosmwasm-vm-js); however this is harder to work with for consuming applications like CWSimulate.

The old implementation for BasicQuerier was temporary and designed to only handle 1 case (in the tests), this adds generic support for query_chain. You must now subclass BasicQuerier and supply your own handleQuery() function, which will get passed the decoded query request. BasicQuerier.query_raw() will delegate and handle the proper encoding of BasicQuerier.handleQuery(), which is toUint8Array({ ok: { ok: toBase64(response) } }), where response is a JSON object containing the query response.

In the future, we will need to provide support for Rust errors, because the Ok(Ok(response)) corresponds to SystemResult<ContractResult<Binary>> (Binary is a CosmWasm Rust type that encodes a struct to Base64 strings in JSON).