U4-5461 - Close date picker once date is selected

This turned out to be a little more tricky than hoped, as the date picker fires a changed event not just when a day is selected, but also when a month is selected but before the day is.  So it wasn't as easy to just hide the picker on the day event.

I've got around this by making a small amend to the date picker itself - adding a parameter of the view mode.  If not passed, or if the current view mode matches the passed one, the picker will hide.  So calling with the view mode of days then gives the right behaviour.

Exactly what date picker and what version is currently in use isn't clear (the minified and non-minified have slightly different comments) - but from what I could find online it's already been slightly amended so already can't be easily upgraded.  Hence this further amend shouldn't change anything on that score.