Have a now button for the date & datetime fields in a form

[boazmohar]

There are some cases where you have a start and end date / datetime fields in a form.
The form is left open while a session / surgery is ongoing.
It would be convenient to add a button that would fill the current date / datetime into the field.

This only effects the date / datetime fields in a form.

[mattbdean]

Here's what it looks like on master