Use common licence attributes from lib/licenses.nix

Many (less easily automatically converted) old-style strings
remain.

Where there was any possible ambiguity about the exact version or
variant intended, nothing was changed. IANAL, nor a search robot.

Use `with stdenv.lib` wherever it makes sense.

pkgs/applications/video/dvdauthor/default.nix

@@ -18,9 +18,9 @@ stdenv.mkDerivation rec{
     ./dvdauthor-imagemagick-0.7.0.patch
   ];
 
-  meta = {
+  meta = with stdenv.lib; {
     description = "Tools for generating DVD files to be played on standalone DVD players";
     homepage = http://dvdauthor.sourceforge.net/;
-    license = ["GPLv2"];
+    license = with licenses; gpl2;
   };
 }