Fix empty stacktrace in bug report

ACRA has to be initialized after MultiDex
https://github.com/ACRA/acra/issues/619
https://github.com/ACRA/acra/wiki/Troubleshooting-Guide#legacy-multidex

app/src/debug/java/org/schabi/newpipe/DebugApp.kt

@@ -1,6 +1,5 @@
 package org.schabi.newpipe
 
-import android.content.Context
 import androidx.multidex.MultiDex
 import androidx.preference.PreferenceManager
 import com.facebook.stetho.Stetho
@@ -11,11 +10,6 @@ import okhttp3.OkHttpClient
 import org.schabi.newpipe.extractor.downloader.Downloader
 
 class DebugApp : App() {
-    override fun attachBaseContext(base: Context) {
-        super.attachBaseContext(base)
-        MultiDex.install(this)
-    }
-
     override fun onCreate() {
         super.onCreate()
         initStetho()
@@ -34,6 +28,12 @@ class DebugApp : App() {
         return downloader
     }
 
+    override fun initACRA() {
+        // install MultiDex before initializing ACRA
+        MultiDex.install(this)
+        super.initACRA()
+    }
+
     private fun initStetho() {
         // Create an InitializerBuilder
         val initializerBuilder = Stetho.newInitializerBuilder(this)

app/src/main/java/org/schabi/newpipe/App.java

@@ -77,7 +77,6 @@ public class App extends Application {
     @Override
     protected void attachBaseContext(final Context base) {
         super.attachBaseContext(base);
-
         initACRA();
     }
 
@@ -200,7 +199,11 @@ public class App extends Application {
                 .build();
     }
 
-    private void initACRA() {
+    /**
+     * Called in {@link #attachBaseContext(Context)} after calling the {@code super} method.
+     * Should be overridden if MultiDex is enabled, since it has to be initialized before ACRA.
+     */
+    protected void initACRA() {
         try {
             final CoreConfiguration acraConfig = new CoreConfigurationBuilder(this)
                     .setReportSenderFactoryClasses(REPORT_SENDER_FACTORY_CLASSES)