[BUG #7228] qx.ui.mobile.form.SelectBox.setSelection method do not produces "changeSelection" event 


* Replaced __selectedIndex through selectedIndex property in menu, for firing event "changeSelection"
* Refactored qx.Mobile Menu
* Updated __selection to property, in SelectBox for firing event "changeSelection" on every property apply.
* Replaced __selectedIndex through selectedIndex property in menu, for firing event "changeSelection"
* Refactored qx.Mobile Menu
* Updated __selection to property, in SelectBox for firing event "changeSelection" on every property apply.