Enable/Disable an Icinga2 Service and create GraphiteWriter object

Similar to Pull #11 

This allows you to specify an array for enabled and disabled features via a parameter under the icinga2::server class.

The features.pp class will check to see if a feature has been added in both arrays and only disable it if it has been.

The enable.pp define will check to make sure the *.conf file exists in features-available before trying to enable it and checks to make sure a file/symlink is created in features-enabled to make sure it does exec multiple times.

Additionally a new object manifest has been added to set the conf file for graphite (GraphiteWriter).
Could you change these names to `graphite_host` and `graphite_port`? Sorry to nitpick, but I want to keep parameter names descriptive, as the module will get tons of parameters as it grows in size.