Add ?launchCounter

[samreid]

During phetsims/density-buoyancy-common#168 it came to our attention that it is difficult to know whether or not a page has crashed an iPad. For instance, if I start fuzzing at 9:10am, then get a coffee and come back to see it is still fuzzing, I may mistakenly think it has not crashed at all. However, platforms such as mobile safari automatically reload on a crash, and so it is possible that the page crashed many times while we weren't looking. @zepumph and I discussed that a query parameter could keep track of the launch count to see the crash rate.

[samreid]

This has been working well enough, closing.