Refactor Launchpad/Stargate/CosmWasm tests

[willclarktech]

Currently our test code for lower-level functionality makes use of higher-level code, like SigningCosmosClient for setting up test situations. This is a real pain when creating a fresh package modelled on this structure, because you have to write all the code before writing any tests that work. Ideally the test code would be more modular so we can get simple things working and tested before writing more complex code.

There's a similar bootstrapping issue with the deployment scripts, where a lot of the tests require a populated blockchain, but the population script requires very high level code already.