Set curl CURLOPT_TIMEOUT to prevent processes being stuck after connecting to server

[FelixJacobi]

We encountered the situation that the HTTP connection was initially established but the cron script using the library hangs afterwards for an infinity time (something was wrong on TCP level). Debugging the issue showed something was wrong with the network link between both machines (fault on side of the ISP). This change adds a reliable timeout for the whole request process in cURL to prevent the library from hanging forever in future if such situation occurs.