[stackedAreaChart] Adding legend stateChange listener and removing old
legend click code.
Converting cumulativeLineChart to use legend stateChange dispatch.
Updated lineChart and stackedArea to update chart.state
whenever legend.stateChange is dispatched.
Updating almost all main chart types to use new legend.stateChange
code. All have been tested.
Updating scatterPlusLineChart.js to use legend.stateChange.