maintain always up-to-date list of proxy servers

[serapath]

@todo

• create a get-proxy-server.js with the logic to fetch proxy server IP's
• add http api to the https://<get-proxy-server.js>:<port>/proxylist
  • on request, read proxylist.json and check timestamp
    • if timestamp is old, fetch new proxies first and save them in proxylist.json with new timestamp
    • if timestamp is good, return proxylist.json content
• when fetching new <proxy ip>s:
  • delete old proxylist.json and create new proxylist.json with new timestamp
  • for each <proxy ip> it gets, try to make a request to e.g. google.com and
    • if it succeeds store <proxy ip> in proxylist.json
    • if it fails, ignore and throw away the <proxy ip>
• make sure it get's started and restarted whenever the digital ocean server starts or restarts

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