Add VideoView to Audio/VideoPlayerActivity

It loads media2-widget library from prebuilts to use latest version of
the library. Please ensure that prebuilts/sdk repo is synced.

Test: Play an audio/video manually
Change-Id: Ib4f306c34366cb8a8d087ee9dbc5c96314f1b6e3
diff --git a/build.gradle b/build.gradle
index a19659a..958133c 100644
--- a/build.gradle
+++ b/build.gradle
@@ -27,8 +27,10 @@
 allprojects {
     repositories {
         jcenter()
-        maven { url 'https://maven.google.com' }
         google()
+
+        // TODO: Remove before releasing and after stable media2 is released
+        maven { url "$rootDir/../../../prebuilts/sdk/current/androidx/m2repository" }
     }
 }