Add KeyManager To HiddenWallet

[nopara73]

https://github.com/nopara73/StratisBitcoinFullNode/tree/keymanagement

It should be before the post-mix wallet is being started working on.
It has locking and labeling built into it, which will be very useful to post-mix wallet.

Its locking must be refactored.

It's using BIP44, that might not be the right decision either.

Depending on how the design of post-mix wallet will be figured out the accounts might get different meaning than the current Bob/Alice accounts.

[nopara73]

Done.