enabling lock wallet feature

[mrdoom4334]

Would be nice if we can lock our wallets

[adityapk00]

This is a good idea, but I'm currently hampered by the lack of support in the underlying zcashd. We'll need to wait for the node to add this feature.

[kimziv]

There is no the features of wallet-locking without a passphrase, so that few people use it. I hope they can implement the feature as soon as possible. Thanks