move pidList logic to single place

This moves the pidList logic to a single file, and also simplifies the syntax (it seemed ugly to have so many places where we were doing App.pidList.push(window.setTimeout).

My editor also removed a bunch of trailing spaces.  My apologies if this makes this diff harder to read.

I got rid of pidList for studio, because it didn't look like it was being used.  It's easy enough to add it back if it is used in the future.

Thoughts?  I'm okay with rejecting this PR as unnecessary, but I feel like it makes things cleaner.