[FIX] point_of_sale: dot input should be recognized even at different lang

Language such as FR recognizes `,` as the decimal separator. However, it is
possible that the keyboard setting is American so the decimal point in the
numpad will send `.` when pressing it. POS should be able to recognize both.
This fix allows `.` sent from keyboard to be interpreted as decimal separator
even at language where the decimal separator is `,`. This is okay because
number inputs in POS doesn't take into account the thousand separator.