Calendar demo submit is broken

[mvorisek]

Steps to reproduce:

1. open demos/form-control/calendar.php
2. click Save

[mvorisek]

No custom UI format per form control should be needed, global (per App) UI persistence should be enough.

[mvorisek]

The problem in the demo is UI persistence date/time format is mutated: https://github.com/atk4/ui/blob/4.0.0/demos/form-control/calendar.php#L20

That is simply a wrong usage, as the form input is processed at once with one UI persistence format, basically mutation of UI persistence formatting after UI persistence is used is not supported and never will be.