Sketch integration test framework

[ethanfrey]

Handle most of the memory items needed (with Cell and Box<dyn Trait>). However, I hit an issue trying to construct the Extern. Ideally we would only need &mut Storage, so I could use RefCell, but that is acceptable. However, passing in Router as the Querier, which is also the execution environment of the contract itself, is impossible.

I basically need &Router and Router at once! If we could loosen Extern to only require &Querier rather than Querier (which is all it actually uses), then this would be much easier to implement in Rust.

Raised issue CosmWasm/cosmwasm#584 (and maybe this code belongs in cosmwasm to iterate closer with the APIs)

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Update: With the 0.12 cosmwasm API this works quite well. More or less code-complete, including bank.

Done:

• Test bank
• Test WasmRouter
• Test Router - move coins, call contract
• Add Reflect check - contract calling others: success + error
• Handle rollback on error (transactional) - handled in Router with rollbacks #134
• Evaluate high level API

This rollback on error is a bit trickier than I thought... it affects cases where one step succeeds (and writes) and a sub-message fails. Maybe I merge this first, then do another PR for that.

[ethanfrey]

@webmaster128

Code is (almost) all implemented as I envisioned it. A number of TODOs and of course this needs tests with real contracts, but the Rust compiler is happy with the lifetimes here.

There is one obvious issue about a contract querying it's own address in handle, which leads to a runtime error. I can add tests to trigger with mock contracts and look at handling that better, but let's discuss this on a call Wednesday first.

[ethanfrey]

I will merge this, as there is quite some work on top #134 and #135 and I haven't gotten a review here. Happy for any comments on this code and I will address it later. But quite some is modified in the other PRs anyway.