Prevent infinite loops in jsbin editor.

This is done by rewriting loop code with a test to see how many times the test has been called.

In general, JS is going to run pretty quick, so an infinite loop can rack up 100,000 iterations pretty quickly. If we hit that limit, we break out of the loop and console.error (note: I'd like to echo this back to the user in the UI somehow - probably the linter notice).

This way the code continues, it's a little slow, but it *doesn't* crash the browser.
Remove all but active iframe on runner. Fixes #687

The old code was expecting a single irame to exist. Because it was only listening to the window.onload, we could render many times but only a single load event would fire. So code changed to search for all iframes, and remove all from the DOM except for 'sandbox.active'.
removed loop test file - need to move to dep
Merge pull request #699 from remy/fix/infinite-loops

Fix infinite loops