Xamarin.Forms - Label Tutorial

Mass update to 4.8. (#650)

* 4.8 code updates.

* Sample updated to 4.8-pre1.

* TextTransform example added.

* Text transform added.

* 4.8-pre2 update.

* Brushes support.

* Don't need to explicitly set GradientStops.

* 4.8-pre3 updates.

* Update to 4.8-pre3

* Update to 4.8-pre3

* New sample.

* Moved file into correct folder.

* Let the default values shine.

* Remove AppTheme experimental flag.

* Samples updated to 4.8.

* Mass update to 4.8.

* Fix UWP build failures.

* Updated designer files.

* Android build fixes.