Add AutofitHelper and AutofitLayout

* Refactored automatically size to fit logic from `AutofitTextView` into a more reusable piece, `AutofitHelper`.
* `AutofitHelper` can be used in Java to enable automatic size to fit on any `View` extending `TextView`.
* `AutofitLayout` can be used in XML to enable automatic size to fit on any `View` extending `TextView`.
bit weird to have all the private attrs in the middle of this file?