Move constants to params

[alpe]

Summary

We have a couple of hard coded values that could be moved into params so that we can update them without deployment.
An incomplete list:

• max contract size
• gas multiplier
• instance cost
• compile cost
  ...

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[ethanfrey]

Great ideas. Use the current constants as defaults and allow governance to adjust it.

[ethanfrey]

Note: I will have to implement CosmWasm/wasmvm#122 before it is safe to change GasMultiplier. Let's wait on this until I update go-cosmwasm

[alpe]

We have closed the PR and postpone this feature

[ethanfrey]

This is related to #809

We need some of these values in the stateless ValidateBasic functions. That will make usage of Params impossible.

As a first step, I would propose pulling them into module-level var rather than const.
Projects importing x/wasm could then customize them either by runtime flags or by setting them explicitly in their custom app.go or cmd/*/main.go

[alpe]

I think we can close this and build a solution with #813.