Harmonize API

[chris-rock]

#49 introduced the separation of client and server config. this is not consistent across all configurations. We need to harmonize the interface while supporting a simple client and server config

[bkw]

Do you mean moving all attributes that only affect the server into the ssh/server namespace?

Also: Does is make sense to split the ipv6-support into two as well? That seems to be the only attribute left that affects both client and server configs, but it also is shared with other hardening cookbooks, so splitting that might be a bit tricky..