Workaround for #558

Adds a check for window.polyfills before calling
window.polyfills.placeholders(). While this doesn't allow the polyfills
to be properly loaded, it does keep the error from occuring.
Better logic for deciding when to reload

What was needed was not to check whether the story model had been
loaded, but instead to update the hasStory property when the story was
initially saved.

Addresses #417