Disable text selection with right click on file tree.

services/web/public/stylesheets/app/editor/file-tree.less

@@ -35,6 +35,10 @@ aside#file-tree {
 			line-height: 2.6;
 			position: relative;
 
+			.entity {
+				user-select: none;
+			}
+
 			.entity-name {
 				color: @gray-darker;
 				cursor: pointer;