after receiving panic trigger, quit remove from history

This makes the app fully exit, and removes it from the Recent Apps listing
with the goal of hiding whatever the user was currently watching, and/or
searching for.

PanicKit provides a common framework for creating "panic button" apps that
can trigger actions in "panic responder" apps.  In this case, the response
is to lock the app, if it has been configured to do so

https://dev.guardianproject.info/projects/panic/wiki

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

@@ -0,0 +1,36 @@
+
+package org.schabi.newpipe;
+
+import android.annotation.SuppressLint;
+import android.app.Activity;
+import android.content.Intent;
+import android.os.Build;
+import android.os.Bundle;
+
+public class ExitActivity extends Activity {
+
+    @SuppressLint("NewApi")
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        if (Build.VERSION.SDK_INT >= 21) {
+            finishAndRemoveTask();
+        } else {
+            finish();
+        }
+
+        System.exit(0);
+    }
+
+    public static void exitAndRemoveFromRecentApps(Activity activity) {
+        Intent intent = new Intent(activity, ExitActivity.class);
+
+        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK
+                | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS
+                | Intent.FLAG_ACTIVITY_CLEAR_TASK
+                | Intent.FLAG_ACTIVITY_NO_ANIMATION);
+
+        activity.startActivity(intent);
+    }
+}