Refactoring to put browser specific code in a new class, BrowserPlatform.
BrowserPlatform implements IPlatform. Chart.Platform is the constructor for the platform object that is attached to the chart instance.
Plugins are notified about the event using the `onEvent` call. The legend plugin was converted to use onEvent instead of the older private `handleEvent` method.
Wrote test to check that plugins are notified about events
added helper method to adjust the index
pass in chartConfig rather than access within method, make it easier to
test
added semi-colon at the end of helper method
added test for adjustIndex helper method
fixed lint issues
added integration test for the interaction of trigger an event over the
bar
.
.
moved adjustIndex into element helper
removed method from helper and adjusted method in core.interaction
added test for the element adjustIndex helper
added a skipIndexAdjustment method to handle when to skip the adjustment
along with test cases
fixed lint issues
removed the test for the helper method
