Add "change_position" option to name_new/firstupdate/update

[JeremyRand]

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

The send RPC method supports specifying the position of the change output via the change_position option. Unfortunately, this option is not supported by the name RPC methods.

Describe the solution you'd like

Add the change_position option to the name RPC methods, so that name transactions have feature parity with currency transactions.

Describe alternatives you've considered

N/A.

Additional context

N/A.