Roll over delegation tokens during voting

[plaidfinch]

The default behavior of the planner should be to "roll over" delegation tokens during voting, to minimize linkability. Doing this means that a vote transaction will be [Vote, Spend, Output] with the output self-addressed to the same address as the note originated. This can't be done if the note being voted with was already spent; in that case, the transaction should just be a vote action.

Originally posted by @plaidfinch in #1795 (comment)