Add HD Wallet integration (temporary and hacky!!!)

Add RPC/Websocket calls for:

getdepositscript
createseries
replaceseries
thawseries
It worries me that we don't have even a single test for any of the new functions here, and it will be quite tricky to write them because it's nontrivial to construct a Wallet instance (which they need) in a test. However, all of them only need the Wallet to get a reference to the Manager, so if you move the meat of those functions into helper functions that take a Manager (instead of a Wallet) as first argument, we should be able to test them and have these ones just call them and pass their retval/errors through.