CustomDialogs example: add an example using Calendar

Also the spinbox exmample will accept when the user presses enter.

Change-Id: I47765899acfbc435e2409f7a30e54e8f041b6e73
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Liang Qi <liang.qi@digia.com>