Draw events to timeline based on start time and row number #48

Fixed issue #48. One _kind of_ breaking change: I added a row field to the event JSON that helps determine where to draw the block. Details are in the code--I'm going to add some comments to the PR so you can see everything that's going on.
Draws the block at a position bases on the startTime and rowNumber instead of stored pixel values. That way, those values don't have to be updated when the change (responsiveness, zoom, etc)