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/servers/sabnzbd/default.nix

@@ -14,6 +14,6 @@ stdenv.mkDerivation {
   builder = ./builder.sh;
   
   meta = {
-    description = "Usenet NZB downloader, par2 repairer and auto extracting server.";
+    description = "Usenet NZB downloader, par2 repairer and auto extracting server";
   };
 }