Widgets with practice stats (for Android)

A small widget to track streak progress on the homescreen and remind when a streak is about to be lost. This has been immensely helpful with maintaining a streak on Duolingo.

Hey, we already have this for iOS but for sure would be nice to bring it to Android too! :)

Merged "Widgets for android" #1064

Having widgets available to display on the home screen (like Duolingo-style ones) would greatly help maintain streaks and encourage more practice with the app.

Merged into "App: Widgets with practice stats (for Android)" #757

Merged "Widgets" #1201