add android course track by harvard (#4600)

* add android course track by harvard

* fix alphabetical order at free courses android

* add author names at android course

* update android to android playlist

* undo removed course

* update playlist url
Co-authored-by: NLarissa <larissa.moura@codeminer42.com>

free-courses-en.md

@@ -92,6 +92,7 @@
 
 * [Android Developer Fundamentals (Version 2) — Codelab](https://developer.android.com/courses/fundamentals-training/toc-v2)
 * [Android Developer Fundamentals (Version 2) — Concepts](https://google-developer-training.github.io/android-developer-fundamentals-course-concepts-v2/index.html)
+* [CS50 2019 - Android Track](https://www.youtube.com/playlist?list=PLhQjrBD2T381qULidYDKP55-4u1piASC1) - David J. Malan (Harvard OpenCourseWare)
 * [Developing Android Apps with Kotlin](https://www.udacity.com/course/developing-android-apps-with-kotlin--ud9012) (Udacity)
 * [Learn how to program: Android](https://www.learnhowtoprogram.com/android) - Epicodus Inc.
 * [Material design](https://material.io/guidelines/)