nix: bump template and t480s-work to nixos 20.03

Notable changes:
* add extraConfig for gpg-agent to define the path to the pinentry-program
* removed X11 session directory activation script

nix/os/profiles/common/system.nix

@@ -30,9 +30,9 @@
   '';
 
   # Fonts, I18N, Date ...
-  fonts = {
-    enableCoreFonts = true;
-  };
+  fonts.fonts = [
+    pkgs.corefonts
+  ];
 
   i18n = {
     consoleFont = "lat9w-16";
@@ -52,12 +52,15 @@
     ln -sfT ${pkgs.bash}/bin/bash /bin/.bash
     mv -Tf /bin/.bash /bin/bash
   '';
-  system.activationScripts.etcX11sessinos = ''
-    echo "setting up /etc/X11/sessions..."
-    mkdir -p /etc/X11
-    ln -sfT ${config.services.xserver.displayManager.session.desktops} /etc/X11/.sessions
-    mv -Tf /etc/X11/.sessions /etc/X11/sessions
-  '';
+
+  # TODO: find out if this workaround is still required from nixos 20.03 onwards
+  # system.activationScripts.etcX11sessinos = ''
+  #   echo "setting up /etc/X11/sessions..."
+  #   mkdir -p /etc/X11
+  #   ln -sfT ${config.services.xserver.displayManager.session.desktops} /etc/X11/.sessions
+  #   mv -Tf /etc/X11/.sessions /etc/X11/sessions
+  # '';
+
   system.activationScripts.lib64 = ''
     echo "setting up /lib64..."
     mkdir -p /lib64