Add "lock_unspents" option to name_new/firstupdate/update

[JeremyRand]

Is your feature request related to a problem? Please describe.

The send RPC method supports a lock_unspents option. Unfortunately, this is not supported by the name RPC methods.

Describe the solution you'd like

Add the lock_unspents field to the options parameter of the name RPC methods, for parity with currency transactions.

Describe alternatives you've considered

N/A.

Additional context

N/A.