gnustep: fixup descriptions, remove punctuation

This is based on @joachifm's review. Reworded description in each of
GNUstep's attributes.

pkgs/development/libraries/gnustep/back/default.nix

···
   };
   buildInputs = [ cairo base gui freetype pkgconfig x11 ];
   meta = {
-    description = "GNUstep-back is a generic backend for GNUstep.";
+    description = "A generic backend for GNUstep";
   };
 }

pkgs/development/libraries/gnustep/base/default.nix

···
   ];
   patches = [ ./fixup-paths.patch ];
   meta = {
-    description = "GNUstep-base is an implementation of AppKit and Foundation libraries of OPENSTEP and Cocoa.";
+    description = "An implementation of AppKit and Foundation libraries of OPENSTEP and Cocoa";
   };
 }

pkgs/development/libraries/gnustep/gorm/default.nix

···
   buildInputs = [ base back gui ];
 
   meta = {
-    description = "Gorm stands for Graphical Object Relationship Modeller and is an easy-to-use interface designer for GNUstep";
+    description = "Graphical Object Relationship Modeller is an easy-to-use interface designer for GNUstep";
   };
 }

pkgs/development/libraries/gnustep/gui/default.nix

···
   buildInputs = [ base ];
   patches = [ ./fixup-all.patch ];
   meta = {
-    description = "GNUstep-gui is a GUI class library of GNUstep.";
+    description = "A GUI class library of GNUstep";
   };
 }

pkgs/development/libraries/gnustep/gworkspace/default.nix

···
   buildInputs = [ back base gui system_preferences ];
   configureFlags = [ "--with-inotify" ];
   meta = {
-    description = "GWorkspace is a workspace manager for GNUstep";
+    description = "A workspace manager for GNUstep";
   };
 }

pkgs/development/libraries/gnustep/make/default.nix

···
   patches = [ ./fixup-paths.patch ];
   setupHook = ./setup-hook.sh;
   meta = {
-    description = "GNUstep-make is a build manager for GNUstep.";
+    description = "A build manager for GNUstep";
 
     homepage = http://gnustep.org/;
 

pkgs/development/libraries/gnustep/projectcenter/default.nix

···
   propagatedBuildInputs = [ base back gui gnumake gdb gorm ];
   
   meta = {
-    description = "ProjectCenter is GNUstep's integrated development environment (IDE) and allows a rapid development and easy managment of ProjectCenter running on GNUstep applications, tools and frameworks.";
+    description = "GNUstep's integrated development environment";
   };
 }

pkgs/development/libraries/gnustep/systempreferences/default.nix

···
   buildInputs = [ back base gui ];
 #  propagatedBuildInputs = [ gnustep_back gnustep_base gnustep_gui ];
   meta = {
-    description = "System Preferences allows to manage the settings of many aspects of the GNUstep environment and its applications";
+    description = "The settings manager for the GNUstep environment and its applications";
   };
 }