Set the number of events to delete correctly

The code was only freeing up to 20 or so events, depending on how many particles the last non-visible event had.  Correctly setting the index to delete-up-to to be the highest non-visible event.
Only splice if there's something to remove
Merge pull request #54 from RaoOfPhysics/master

Changes to research description
Update image links
Merge pull request #57 from cgeorg/patch-1

Set the number of events to delete correctly
Prevent user from selecting DOM element when clicking detector