* Wallet passphrase lock fixes:
- wallet should not allow cli commands to bypass lock validation
- wallet should lock again in mixing mode if it was unlocked for mixing and next unlock (e.g. for sending funds) happened
- removed AnonymizeOnlyUnlocked status, it's never going to be reached anymore
- "For anonymization only" checkbox:
- should be available only when user click "Start Mixing"
- should be set on by default when available
- adjusted title
- adjust error messages in walletpassphrase for unlocked wallets
* Add comment about IsLocked() usage
* Final safety check for locked wallet in WalletModel::prepareTransaction
