kdeFrameworks: fixup inputs and outputs

- Reduce environment pollution with a separate $bin output containing programs,
  plugins, and shared data. Libraries remain in $out and are not installed into
  the environment.
- Only propagate build inputs as required.

pkgs/desktops/plasma-5/kscreen.nix

@@ -6,8 +6,8 @@
 mkDerivation {
   name = "kscreen";
   nativeBuildInputs = [ extra-cmake-modules ];
-  propagatedBuildInputs = [
-    kglobalaccel ki18n libkscreen qtdeclarative qtgraphicaleffects kconfig
-    kconfigwidgets kdbusaddons kwidgetsaddons kxmlgui
+  buildInputs = [
+    kconfig kconfigwidgets kdbusaddons kglobalaccel ki18n kwidgetsaddons kxmlgui
+    libkscreen qtdeclarative qtgraphicaleffects
   ];
 }