Allow ticket buying wallets to set an xpub for a voting wallet instead of reusing the voting address

[jrick]

This improves privacy and security by using a different address/key for each ticket and it's corresponding vote/revocation.

If not hiding the key using P2SH in the ticket purchase, there is nothing to change on the voting wallet side as it will stay in sync with newly used addresses. On the ticket purchasing side, the child index for the xpub needs to be incremented after every ticket purchase. The simplest way to implement this would be to check the address used dcrd index to find the next child index of the xpub to use, similar to how accounts are scanned on startup.

[kLkA]

Hi @jrick . Can I take this task into work?

[jrick]

sure