Extensible works great on ExtJs 4.2.0!

Even in Neptune theme, great work.

I fixed a minor issue, my console reported a warning:

    called with an undefined className: undefined app.js:30
        console.trace() app.js:31
            consoleLogger app.js:31
            Ext.override.addCls.addWithClassList ext-dev.js:20517
            Ext.define.handleDayMouseEvent AbstractCalendar.js:2134
            Base.implement.callParent ext-dev.js:6912
            Ext.define.handleDayMouseEvent Month.js:599
            Ext.define.onMouseOver AbstractCalendar.js:2071
            (anonymous function)
            wrap