fix(grid): improve drag clue layout

The drag clue size is calculated for content-box, which breaks whenever the Bootstrap framework is included.

scss/grid/_layout.scss

@@ -347,6 +347,7 @@
         align-items: center;
         align-content: center;
         vertical-align: top;
+        box-sizing: content-box;
 
         .k-link,
         .k-button.k-bare {