JS helper: Wrap multisig support

[grod220]

The javascript companion to the CLI equivalent functionality: #44. This allows for Wraps to be done in a multisig setup.

The chief workflow is:

• All multisig holders run the multisigOfflineSignWrap() function and pass the result to the final broadcaster. The payer must also execute this function.
• All results are passed to multisigBroadcastWrap() where it is validated, combined together, and broadcast to the network.

Contains an example that executes these steps.

[mcintyre94]

I've left some comments, a lot of them are just style things that I think will make it a bit easier to maintain this.

But overall I think these helpers are doing a little too much, and should just be focused on returning a transaction to the caller. I'd cut out all the code that sends/confirms transactions, and let the caller re-use whatever logic they're using elsewhere in their app.

I might not be completely understanding the expected use case here, but since this is part of a @solana-program lib I think it likely makes sense for it not to be concerned with things like sending transactions.

[grod220]

@mcintyre94 very helpful review! Implemented your feedback. Think it makes lots of sense.

[mcintyre94]

This looks good to me! I think this is the right interface now and it all looks good. The only thing I'd suggest is getting rid of the arrow functions, because we don't usually use them in our libraries or the generated clients. And making sure all the functions have a return type.