Add support for chart events

[byronwall]

Saw this interesting article which I think can provide a lot of add'l functionality for charts. It describes how to tap into the events that charts expose. One of the major things to test is the ability to click to zoom the chart. I am also curious if this will resolve some of the issues with determine which chart is selected. Currently the add-in cannot determine that a Chart is selected if the selected part of it is an Axis.

I'll work this in a new branch and then see what wiring is needed to interface the events with the current code.