Prevent selection of diff line numbers (#2240)

public/css/index.css

@@ -2069,6 +2069,10 @@ footer .ui.language .menu {
   color: #A7A7A7;
   background: #fafafa;
   width: 1%;
+  -moz-user-select: none;
+  -ms-user-select: none;
+  -webkit-user-select: none;
+  user-select: none;
 }
 .repository .diff-file-box .file-body.file-code .lines-num span.fold {
   display: block;

public/less/_repository.less

@@ -913,6 +913,10 @@
 				color: #A7A7A7;
 				background: #fafafa;
 				width: 1%;
+				-moz-user-select: none;
+				-ms-user-select: none;
+				-webkit-user-select: none;
+				user-select: none;
 
 				span.fold {
 					display: block;