[FIX] point_of_sale: make receipt screen touch scrollable

In the POS we use a touchmove event listener to stop undesired
rubberbanding (in Chrome.disable_rubberbanding()). Elements which should
be scrollable by touch should have the touch-scrollable class. The
receipt screen is obviously one of those, because otherwise you won't be
able to scroll down if you have a long receipt.

opw-670899

addons/point_of_sale/static/src/xml/pos.xml

@@ -652,7 +652,7 @@
                         <i class='fa fa-angle-double-right'></i>
                     </span>
                 </div>
-                <div class="centered-content">
+                <div class="centered-content touch-scrollable">
                     <div class="button print">
                         <i class='fa fa-print'></i> Print Receipt
                     </div>