new icon and css for add

I use the action add (as in add new) in my app

Author: Felipe Figueroa

src/images/page_white_add.png

@@ -94,6 +94,7 @@
 .context-menu-item.icon-copy { background-image: url(images/page_white_copy.png); }
 .context-menu-item.icon-paste { background-image: url(images/page_white_paste.png); }
 .context-menu-item.icon-delete { background-image: url(images/page_white_delete.png); }
+.context-menu-item.icon-add { background-image: url(images/page_white_add.png); }
 .context-menu-item.icon-quit { background-image: url(images/door.png); }
 
 /* vertically align inside labels */