Add KeyChainGroup.isDeterministic() and Wallet.isDeterministic(). Add static constructor for non-HD wallets.

Paper wallets are neither HD nor non HD. They're just a key. You could import it into the users regular wallet and it'd work just fine if we had a better fix for replaying. If you create a separate Wallet just for that key, that works OK even if it has an HD chain created. It wastes a bit of memory but is otherwise not a problem.

A fresh wallet should become HD the moment you request an HD key from it via current/fresh* - so in that sense there's no real difference.