Set sortable on table header instead of label

This way the cursor is rendered as pointer over the clickable element.

sao/src/sao.less

@@ -872,6 +872,10 @@ img.icon {
             position: relative;
             padding: 5px;
 
+            &.sortable {
+                cursor: pointer;
+            }
+
             > label {
                 display: inline-block;
                 overflow: hidden;
@@ -880,9 +884,6 @@ img.icon {
                 margin: 0;
                 vertical-align: bottom;
 
-                &.sortable {
-                    cursor: pointer;
-                }
             }
 
             > div.resizer {

sao/src/view/tree.js

@@ -239,7 +239,7 @@
                         }
                         this.sort_model(e);
                     });
-                    label.addClass('sortable');
+                    th.addClass('sortable');
                 }
                 tr.append(th.append(label));
                 let resizer = jQuery('<div/>', {