package .desktop files for map editor on Linux, too

move desura scripts into packaging sub-directory

packaging/linux/openra-editor.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Type=Application
+Version=1.0
+Name=OpenRA Map Editor
+GenericName=Tile based RTS game map editor
+Comment=Import legacy maps and create new ones from scratch
+Icon=openra-editor
+Exec=openra-editor
+Terminal=false
+Categories=Game;StrategyGame;