UrlCodeHints should not try to handle filesystem changes until after appReady

This pull request just moves the filesystem change handler registration from the module scope to the `appReady` event handler. When the change handlers are registered in the module scope, it's possible to get a `ReferenceError` by trying to clear a property on the `CodeHintProvider` before it has been defined. 

I screwed this up during the filesystem merge. Sorry!