Support multiple messages in CanExecute query

[maurolacy]

Closes the last part of #145, supporting multiple messages in CanExecute query.

[orkunkl]

Only one comment. LGTM

[ethanfrey]

Since making queries is rather cheap and we now have a rather awkward Vec<CosmosMsg> -> Vec<bool> API, I wonder if this is actually useful. I am fine with the rename, but wonder about this API change.

The default case is just sending one message, and this makes that case noticibly more awkward.

[webmaster128]

It is also a question how inteligent the query API is expected to be. What happens if you pass a bunch of bank send messages that are fine individually but together exceed the allowance.

What's the purpose/use case of this API at all?

[ethanfrey]

The general idea was a generic way to query "can I do this?" without relying on the specifics (allowances/permissions only in cw1-subkeys). And yeah, it was not designed to be smart and handle messages interacting.

I don't know if there will be other approaches than cw1-subkeys. But this was a way to generically query "am I allowed to send 100 Atoms?" before doing so (which could help in generic UIs).

This can be removed and added later. Or just not supported in clients. I don't see adding more complexity here as beneficial.

(I almost consider making execute only take CosmosMsg, not Vec<CosmosMsg>, but that may be too restrictive.

[maurolacy]

It is also a question how inteligent the query API is expected to be. What happens if you pass a bunch of bank send messages that are fine individually but together exceed the allowance.

Good point. Since the checks are stateful, it seems to me that to support this API we would need to reproduce the state changes to be able to validate the sequence of messages. Which may be difficult / costly to do.
That, or we just support one message per query, as of now.

What's the purpose/use case of this API at all?

Tests look nicer / simpler, but I agree, that's not enough of a use case to justify this.

[maurolacy]

Not merging because impl not stateful when checking multiple messages. Better to provide simpler, clearer API.