enable ARC for the iTunes plug-in
fix warnings
sort out the problem with missing icons

* handle them like all other icons in Quicksilver (using QSResourceManager)
* remove iTunes DJ/Party Shuffle icon references
* built against Quicksilver 1.1.0 and will require that version
bump version to 2.4.2

(the build number was already increased by @tiennou in a previous commit)
\r → \n
switch iVars to properties in QSiTunesDatabase
switch iVars to properties in action providers
switch iVars to properties in object sources
Merge pull request #19 from quicksilver/arc

convert to ARC