Column Click Events & Minimum Viewable Area

Hey first of all let me say I really appreciate your work on this and it was exactly what I was looking for. I had a few use cases that it wasn't serving my needs for so I added some features. Let me know what you think, I came at this with 2 goals
1) Fix my problems
2) Not break your code

So hopefully I achieved those goals. The commit messages should describe my changes well but the overview is 
1) add a data attribute to use instead of the loadData function (left the loadData function as goal #2) . This seems more natural to me, though I can understand that because it does a full clear and reload it might not be the most efficient way to do it (there is much room for optimization).
2) Make it possible to add data to a gantt. There were 2 problems I ran into, 1) when clicking a row you couldn't tell what cell you clicked. I addressed this by adding on-column-clicked and adding endDate property to the column (also created a column class). 2) If there was no data the Gantt chart wouldn't be visible so I added a fromDate and toDate attribute allowing you to specify the minimum values shown (this doesn't truncate data though so if a task is specified before or after the params are ignored). I might change this behavior in the future

I would definitely like to see this change merged in so if there is anything I can do to make this more palatable to you let me know. I did test your demo code and all appears to be working.