Add tests that check whether changing the toggle state of a button is propagated to the corresponding element in the overflow popup.
Add uid to all of the buttons that are children of a buttonGroup. Expose toggle method. Fix telerik/kendo#3405
Minor refactoring changes. Extract kendo.attr(uid) as a constant.
SplitButton id is assigned to the main button, SplitButton's wrapper and popup element receives ID with suffix. Fix telerik/kendo#3413