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

Just a key is non-HD with one imported key.

Anyway, the API is less confuzing if it allows the user to specify what he wants. And not change state behind the users back. Auto-upgrading is nice if you really want it. If not, it's just scary and confusing. So what's the problem clear speaking constructors?