Update OneDaySliderItem

So resizing only the slider gap width resizes all the items
inside the canvas accordingly.

Change-Id: I072569875ae756d6c67440526cf26c2392877bf5
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Update date time handling

Limit strings manipulation by using Date instead. Use system
locale to retrieve date and time formats to display.

Change-Id: Ib9b3be727546a031bcb9c8f231fa77091bdc7587
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>