Add ability to show column or row charts stacked by percent

[kanserh]

Ability to show stacked column/row charts as percent. This option is only necessary if the end user has the Stacking ability turned on. According to Nik on Flowdock this can be achieved in the plotOptions by setting stacking to 'percent' (see below).

plotOptions: {
bar: {
stacking: 'percent',
dataLabels: {
enabled: false
},
showInLegend: true,
colorByPoint: false
}
}