Chargepoint call request

[gjdenhertog]

I think that the OCPI implementation misses the single chargepoint call. I can think of numerous situations in which an application would want to get the status of a chargepoint and/or the details of a chargepoint by its id. Therefore I suggest to add a chargepoint call with a GET function that accepts a chargepoint identifier and possibly a list of identifiers to get the details of multiple chargepoints.