Added more parameterising for sshd_config options

Added some more parameterising for sshd_config options which we need in Aachen.
All new parameters are set to the same default values like given in sshd_config.erb.
Nothing will change if you don't make use of the new parameters.

I have never worked with spec testings before, please double check ./spec/classes/init_spec.rb

Thanks & have phun
Phil