after receiving panic trigger and locking app, remove from history

This makes the app fully exit, and removes it from the Recent Apps listing.

app/src/main/AndroidManifest.xml

@@ -108,6 +108,7 @@
             <category android:name="android.intent.category.DEFAULT" />
           </intent-filter>
         </activity>
+        <activity android:name="com.keepassdroid.ExitActivity" android:theme="@android:style/Theme.NoDisplay"></activity>
         <activity android:name="com.keepassdroid.settings.AppSettingsActivity"
             android:theme="@style/NoTitleBar"></activity>
         <activity android:name="com.keepassdroid.GeneratePasswordActivity"

app/src/main/java/com/keepassdroid/ExitActivity.java

@@ -0,0 +1,36 @@
+
+package com.keepassdroid;
+
+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);
+    }
+}

app/src/main/java/com/keepassdroid/PanicResponderActivity.java

@@ -23,6 +23,7 @@ protected void onCreate(Bundle savedInstanceState) {
         if (intent != null && PANIC_TRIGGER_ACTION.equals(intent.getAction())) {
             App.setShutdown();
             setResult(KeePass.EXIT_LOCK);
+            ExitActivity.exitAndRemoveFromRecentApps(this);
         }
 
         if (Build.VERSION.SDK_INT >= 21) {