Datetime picker library issues (WIP)

[vfonic]

NOTE: This PR only adds failing test and is not ready for merging.

There are several bugs with the datetime picker library.

It's unfortunate that it uses PHP's strftime options, while we use ruby's strftime options (for obvious reasons) on the
backend.

I've added one failing spec to demonstrate one of several issues I've encountered with this datetime picker library.
Here's the screenshot:

The issue is that the frontend js library doesn't parse the ruby's formatted date.

Here are some other "interesting" issues:

1. format_time doesn't work when specified in config so it has to be specified on every input field
2. The datetime picker library is using wrong date formatter library version. It claims to be using one version,
   while it actually uses a different version. More info:
   Format "m/d/Y h:i a" changes hour onBlur xdan/datetimepicker#596

My advice would be to switch to another solution completely. These are just not compatible.