New Font Support in Android O

Calligraphy is dead: https://twitter.com/chrisjenx/status/865273111129726977. 

See [the new approach here](https://developer.android.com/preview/features/working-with-fonts.html#fonts-in-xml)

- [ ] Update [TextView guide](http://guides.codepath.com/android/Working-with-the-TextView#using-custom-fonts)

