Multiple sshd configs, solves #233

[joernott]

This pull request implements a solution to issue #233. As we also need to handle one or more additional instances of sshd as sftpserver, I split the monolithic init.pp into several pieces while preserving backwards compatibility.

• package.pp manages the package installation, it is called by init.pp and required by the new instance.pp
• service.pp is now a defined type handling the service, its used by inid and instance
• sshd_config.pp is now a defined type and used by init and instance
• service_instance.pp creates a new systemd service (as I don't have access to Solaris, I can't add support for something comparable, however, the code is prepared for it)
• instance.pp is a wrapper to create a new sshd_config (sshd_config.$title), a service_instance and manages the service for that instance.

[ghoneycutt]

The vast majority of use cases is to not run multiple instances so I think this would really add complexity. The module already lets you write multiple config files so you could implement service management at the profile level for the multiple instances.