Share overreport fix

Features

• Stale/Dup/Low percentages are now shown at main powerpool stats endpoint for convenience
• Hashrate on /clients stats endpoint is now correct
• process title for powerpool can now be set with new configuration value procname. Make sure you install the new requirements!

Bugs

• Shares were being overreported because of the timing jitter optimization being slightly mis-implemented. Overreporting was random, so shouldn't effect payout fairness, but does inflate share counts and hashrates...