[BUG #7710] use box-sizing mixin
[BUG #7710] moved initialization from constructor to init method
[BUG #7710] added initWidgets method
[BUG #7710] new app: qx.Website Widget Browser
[BUG #7710] moved initialization from constructor to init method
[BUG #7710] set default value in init method
[BUG #7710] more demos