Fix issue on debian incron package installation where service name is `incron` instead of `incrond`

Add incron::params class to set the service name to `incron` for osfamily = debian. The service name defaults to `incrond` to maintain backwards compatibility. Resolves #6

- add params and define service name for Debian as incron and default to incrond for all other osfamilies
- remove trailing spaces on manifests/init.pp:19