Clean up name delegation in the plugin. A few rules:

* Each configuration should have its own `name` and `normalizedName` instance
* Debian/Rpm delegate to Linux which delegates to project name.
* Universal has its own name, which is used for generating BASH/BAT files
* Separate key for the package filename now
* Windows has its own name/normalized name which delegates to raw.

Fixes sbt#188

src/main/scala/com/typesafe/sbt/packager/universal/Keys.scala

@@ -5,6 +5,7 @@ package universal
 import sbt._
 
 trait UniversalKeys {
+  val packageFilename = SettingKey[String]("package-filename", "The base filename for the universal packages.")
   val packageZipTarball = TaskKey[File]("package-zip-tarball", "Creates a tgz package.")
   val packageXzTarball = TaskKey[File]("package-xz-tarball", "Creates a txz package.")
   val packageOsxDmg = TaskKey[File]("package-osx-dmg", "Creates a dmg package for OSX (only on osx).")