- Use mempool on gva payments by default (thanks @poka)
- Don't shuffle the gva node list to select the current gva.
Instead, use errors/latency/currentBlock to select the best one.
- Use the best gva when no payment is in process.
- Use the same gva node in subsequent payments.
- Reset current gva node is no other gva payment is in process
- Increase gva node errors on payment errors