Better names for keys/certs

[c0c0n3]

Configuration entry names for DAPS related keys/certs are confusing and not well documented.

Gernot's proposal:

connector_private_key... (as i.e. xxxx.key)...
connector_certificate...(as i.e. xxx.cert)...
and daps_certificate... (as i.e. dapsaisec.cert) ...
to have a reference to the files provided...

And if it is only a part of the whole file to cut out, we should describe that.

and as we're at it, we should also find a better name for idsa_public_key

[c0c0n3]

Probably best to tackle this issue alongside #15.