Implement way to allow users to handle CallErrors

[OrangeTux]

Currently ChargePoint.call() returns None when the remote end returns a CallError. That is because ChargePoint.call() silences the CallError.

This is problematic when one wants to act upon receiving a CallError.

I'm not sure yet how and where to change the code so one can handle CallErrors. The easiest way is to change the body of ChargePoint.call() to this:

if response.message_type_id == MessageType.CallError:
    raise response.to_exception()  

But this change is not backwards compatible. In existing code bases one users of this library might need to wrap all there calls to ChargePoint.call() inside try/except to avoid their code from breaking, like:

try:
   self.call(call.HeartbeatPayload())
except ocpp.exceptions.OCPPError as e:
   pass

[OrangeTux]

In order to main backwards compatibility I suggest to add a keyword argument suppress to ChargePoint.call() that defaults to True.

[tropxy]

Fixed in Raise exception if response from call() is CallError #124