plasma5Packages: alias to the libsForQt5 used to build the plasma5 desktop

For in NixOS it is beneficial if both plasma5 and pam use the same Qt5
version. Because the plasma5 desktop may use a different version as the
default Qt5 version, we introduce plasma5Packages.

pkgs/applications/networking/browsers/firefox/wrapper.nix

@@ -5,7 +5,7 @@
 , flashplayer, hal-flash
 , ffmpeg, xorg, alsaLib, libpulseaudio, libcanberra-gtk2, libglvnd
 , gnome3/*.gnome-shell*/
-, browserpass, chrome-gnome-shell, uget-integrator, plasma5, bukubrow
+, browserpass, chrome-gnome-shell, uget-integrator, plasma5Packages, bukubrow
 , tridactyl-native
 , fx_cast_bridge
 , udev
@@ -76,7 +76,7 @@ let
           ++ lib.optional (cfg.enableTridactylNative or false) tridactyl-native
           ++ lib.optional (cfg.enableGnomeExtensions or false) chrome-gnome-shell
           ++ lib.optional (cfg.enableUgetIntegrator or false) uget-integrator
-          ++ lib.optional (cfg.enablePlasmaBrowserIntegration or false) plasma5.plasma-browser-integration
+          ++ lib.optional (cfg.enablePlasmaBrowserIntegration or false) plasma5Packages.plasma-browser-integration
           ++ lib.optional (cfg.enableFXCastBridge or false) fx_cast_bridge
           ++ extraNativeMessagingHosts
         );