More description fixes

* Remove package name
* Start with upper case letter
* Remove trailing period

Also reword some descriptions and move some long descriptions to
longDescription.

I'm not touching generated packages.

pkgs/applications/video/quvi/scripts.nix

@@ -12,7 +12,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ pkgconfig ];
 
   meta = { 
-    description = "Quvi is a web video downloader.";
+    description = "Web video downloader";
     homepage = http://quvi.sf.net;
     license = "LGPLv2.1+";
     platforms = stdenv.lib.platforms.linux;