Store 24-hour limits per IP / address into file on persistent storage to survive restarts

[lemois-1337]

With 9a79efb we've added per IP / address usage limits. It would be great enhancements if these limits are stored on persistent storage in a file and read after startup of the faucet so that they survive service restarts and system reboots. The same should be stored with the list of recent transactions so that they will be loaded again after restart.