New RPC getparkvotes <block height> <block quantity>

We need an RPC that will allow us to see the state of ongoing interest rate votes as well as historical votes, similar to what we have already done with motions and custodial grants.

The RPC should return a count of how many blocks voted for a particular rate, ordered by rate ascending. Preferably rates would be listed as satoshis and their annual percentage equivalent. There should be a set of results for each duration period that has any votes.

Shareholders are voting now for interest rates to be used as an initial promotion of NuBits and a demonstration of how parking works, so this would be really useful now.

Shouldn't we display the share days destroyed instead of the block count? It's this data that is used in the park rate calculation.

Preferably rates would be listed as satoshis

I'd rather display that in NuBits (NuBits granted per Nubits parked). No other command uses satoshis and I don't think people are expected to know how much a "nu satoshi" is worth.

Solution proposed in pull request #122

Pull request merged.