[FIX] point_of_sale: force numpad to appear next to actionpad

The sizes of these UI elements are all fixed and non-responsive and
everything is supposed to fit. Currently however Firefox (at least
50.1.0 up to nightly 53.0a1) is computing the width of a <br> element to
be 0.0166626px, forcing the numpad to wrap to the next line. This forces
the numpad to be 216px wide (width of 4 buttons at 54px each).

addons/point_of_sale/static/src/css/pos.css

@@ -701,6 +701,7 @@ td {
     display: inline-block;
     float: right;
     text-align: center;
+    width: 216px;
     margin: 16px;
     margin-top: 8px;
     margin-left: 0px;