feat #305 remobe useless code

Ages ago we removed .bindableProperties from widgets. Unfortunately we forgot to remove it from all classes.
This does some cleaning of dead code.
feat #285 Created a simple HTML checkbox widget
fix #315 AutoComplete JS error when clicking the dropdown button

Fixing a regression after b1eb1323439bc3f3203ef5b0c3880410105e8715 using
the similar solution as in 1c8d106816f790fa65465660ee9a6b9ab375af50.

Pull request #316.