refactor: refactor sign method to allow unidentified lock scripts

[Keith-CY]

The sign method is refactored to allow unidentified lock scripts
while skipped lock scripts are prevented outside the sign method

Notice that skipped lock scripts validation is not adopted when
a multisig transaction because it's explictly thrown
when no private key is found. It may be intended.

[yanguoyu]

I guess the offline sign will throw an exception because the input is out of Neuron's control. But other transactions' input is created by Neuron, so the inputs's private key can be found in the wallet.

[Keith-CY]

I guess the offline sign will throw an exception because the input is out of Neuron's control. But other transactions' input is created by Neuron, so the inputs's private key can be found in the wallet.

In terms of functionality, I think a partial-signed transaction should be allowed for offline sign because it is allowed in "online" sign

[Keith-CY]

I guess the offline sign will throw an exception because the input is out of Neuron's control. But other transactions' input is created by Neuron, so the inputs's private key can be found in the wallet.

My bad, it should be "Notice that skipped lock scripts validation is not adopted when
offline-sign sign a multisig transaction because it's explictly thrown
when no private key is found. It may be intended."