Bug 31039: (follow-up) Wrap jQuery in $(document).ready()

Bug 31039: (follow-up) Wrap jQuery in $(document).ready()

cashup_modal.js consists only of jQuery code, so the whole thing should
be contained in a $(document).ready() function. This may or may not be
contributing to the behavior this bug is trying to fix.

Please note that this patch contains whitespace changes, so diff
accordingly.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>