Add display of starting sort letter on screen when scrolling in android TV client

[Deathsquirrel 741]

The Fire TV lets me scroll much faster than the UI can render movie posters.  If possible it would be great if, when scrolling, the screen showed a large letter showing where you were at in the movies alphabetically.  So when you're zipping through Star Wars films faster than it can render them there is a big S on the screen. as an example.