kwallet: Rename to kwalletmanager

Upstream renamed this package:

http://lists.kde.org/?l=kde-i18n-doc&m=139215908204279

pkgs/desktops/kde-4.12/kde-package/4.12.4.nix

···
     { name="kgpg";  }
     { name="kremotecontrol";  }
     { name="ktimer";  }
-    { name="kwallet";  }
+    { name="kwalletmanager";  }
     { name="print-manager"; sane="print_manager"; }
     { name="superkaramba";  }
     { name="sweeper";  }