Dialer: Fix LetterTileDrawable for all languages

* Currently alphabet tile is rendered only for english language.
  However, Google Dialer / Googler Contacts do support rendering
  for all languages. Let's do same here!
* Also, following Google, we do not want to handle numbers.
* Fixes: https://github.com/crdroidandroid/android_packages_apps_Dialer/issues/9



Change-Id: I68bf9f4b80f58f64c1353ce81873d5c0d446bbd6
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>