Do not hardcode everything, use variables. More specifically:

 * make unbound::remote inherit unboud::params
 * introduce a group parameter to params, for all OS/Distributions
 * use the variables throughout unbound::remote

 Note: it now defaults to configure the certificates in unbound.conf,
 instead of leaving those out, as it was before.

 Tested with unbound 1.5.0, and 1.4.22