add public, auto_create flags for wdg

Signed-off-by: Yakov Goldberg <yakov.g@samsung.com>
Add context main window

   - if some window is set as "main", it will be shown;
     if not, will be shown each win, which is auto_creted

Signed-off-by: Yakov Goldberg <yakov.g@samsung.com>
add callback to create widget in simulation

Signed-off-by: Yakov Goldberg <yakov.g@samsung.com>