Unify linux script replacements #182
Migrate linux install location defaults into the Linux section of the plugin.

* Before linux installation details were in the GenericPackageMappings
* Now, we include template generation for linux control scripts in the linux plugin.
  This means, we need the settings we depend on in the more generic location, as
  not all usages of the plugin will include the generic mappings.

Review by @muuki88
Merge pull request #192 from sbt/wip/unify-linux-replacments

Unify linux script replacements #182