Add default API keys to credentials

[epenet]

Implement #54

[jamesremuscat]

I'm not going to merge this.

Not having those keys included in this repository is deliberate: I can then say "pyze does not contain Renault's private API keys". Though at this point I doubt anyone from Renault cares, I'd still prefer to have that as a fallback position.

#54 specifically talked about "the getting of the api-keys into pyze automatically" - e.g. a mechanism for pyze to retrieve the keys from Renault's server where they're (still) publishing them.