parse URL instead of explicit host param

[matth-x]

This PR changes the signature of mocpp_initialize(const char *host, ...). Instead of an OCPP host, port and URL, it expects the OCPP backend URL and the chargeBoxId. This aligns better with the typical instructions of OCPP backends.

For example, the previous notation

const char *host = "my.instance.com";
uint16_t port = 8443;
const char *url = "wss://my.instance.com/steve/websocket/CentralSystemService/charger001";

mocpp_initialize(host, port, url);

becomes

const char *backendUrl = "wss://my.instance.com:8443/steve/websocket/CentralSystemService";
const char *chargeBoxId = "charger001";

mocpp_initialize(backendUrl, chargeBoxId);