Persist events on month changes
Persist events on month changes

Because React reuses event objects by the time the event reaches
the onPrev/NextMonthClick callback all of the attributes are null.

This change has React persist the events so that they can actually
be used in the callback.

gpbl/react-day-picker,orokos/react-day-picker,Fnatte/react-day-picker,majapw/react-day-picker,nonmanifold/react-day-picker,majapw/react-day-picker,zuhairnaqvi/react-day-picker,joeybaker/react-day-picker,nonmanifold/react-day-picker,orokos/react-day-picker,zuhairnaqvi/react-day-picker,ntdb/react-day-picker,ntdb/react-day-picker,chaosmaple/react-day-picker,chaosmaple/react-day-picker,Fnatte/react-day-picker,gpbl/react-day-picker,joeybaker/react-day-picker,saenglert/react-day-picker,gpbl/react-day-picker