build-clients: check if contracts are already created and using correct wasm hash

[chadoh]

Follow-up to #42

Our handle_contracts logic currently assumes that it is being run for the first time. Right now, it will:

1. run contract install --wasm path/to/some.wasm to get the current wasm binary on-chain
2. run contract deploy --wasm-hash [return value of step 1] to create a new contract using this hash
3. run contract bindings typescript for this newly-created contract
4. overwrite the src/contracts/[contract name].ts file with the new contract ID from step 2

Instead, it should:

1. run contract install --wasm path/to/some.wasm to get the current wasm binary on-chain. Yes, this is the same first step. This operation is idempotent, meaning it will always return the same hash for the same wasm blob.

2. check if we have an alias saved for this contract (this depends on the recenly-added alias logic)

3. if no alias, proceed as we currently do, but save the alias on the contract deploy step so we can use it next time

4. if we have an alias, check if the contract with that ID is using the wasm hash generated in step 1. if so, then we're done.

5. if we need to update the contract with the new code, we have a decision to make. Do we deploy a new contract, for simplicity? Maybe for now, assuming that we'll be using this in local & other test networks, that's the most straightforward option. And maybe for production environments and/or live networks, we throw an error for now. Because what really should happen is that we update the contract with the new code and make sure we run any relevant migrations and, and, and...

   We should probably integrate with smartdeploy to help us handle this more complicated update strategy?