[FIX] point_of_sale: no need for disableRubberbanding

The primary goal of disableRubberbanding is to disable scrolling during
touch event by default and to allow only selected descendants to have scrolling
active during touchstart+touchmove event. Only elements with class="touch-scrollable"
are allowed for touch scrolling. This restriction can be a good idea but it
results to bug-ridden explicitness which is not necessary because scrolling
should be allowed automatic by default in the first place. In this commit, we
allowed scrolling by default by:

1. We remove disableRubberbanding.
2. We set the position property of .pos to fixed. This is to accomplish the
original goal of disableRubberbanding (fixing the root element in its position).
3. We remove the touch-scrollable class as they are not needed anymore and
no style associated to it.

Removing the disableRubberbanding method also fixes the Intervention error during
touch scrolling event. The reason for that error is we are calling preventDefault
in the event that is passive. touchmove and touchstart events are passive by default
- which means that preventDefault won't work.

X-original-commit: 54f7fb49dae3aab6a005402a1ac60262bbd15edc