[WIP] bound-ff helper

- [x] Initial demo of how to piggyback on `boundIf` helper logic
- [ ] Convert tests to expect helper to now use a `SimpleHandlebarsView`
- [ ] Does this still work in Ember v1.8.0+ due the [view layer/helpers rewrite](https://github.com/emberjs/ember.js/commit/f839dcd89ad5ecc50d5403a06f507449380557b0) to use `Streams` instead of bufffers?