Converted selectall.css to less for better import

src/UI/Content/Backgrid/selectall.less

@@ -0,0 +1,13 @@
+/*
+  backgrid-select-all
+  http://github.com/wyuenho/backgrid
+
+  Copyright (c) 2013 Jimmy Yuen Ho Wong and contributors
+  Licensed under the MIT @license.
+*/
+
+.backgrid {
+  .select-row-cell, .select-all-header-cell {
+    text-align: center;
+  }
+}