[Android] Simplified AndroidManifest.xml file and properly finish act…

…ivity on back button event.

- Removed redundant attribute "android:label" from activity node; It's already specified for application node.
- Removed nodes irrelevant for the examples: "allowBackup" and "fullBackupContent".
- Invoke ANativeActivity_finish() when back button event is recognized to properly close the application.

examples/Cpp/ExampleBase/Android/app/src/main/AndroidManifest.xml

@@ -5,16 +5,13 @@
 
   <!-- This .apk has no Java code itself, so set hasCode to false. -->
   <application
-      android:allowBackup="false"
-      android:fullBackupContent="false"
       android:icon="@mipmap/ic_launcher"
       android:label="@string/app_name"
       android:hasCode="false">
 
     <!-- Our activity is the built-in NativeActivity framework class.
          This will take care of integrating with our NDK code. -->
     <activity android:name="android.app.NativeActivity"
-              android:label="@string/app_name"
               android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
               android:launchMode="singleTask"
               android:configChanges="orientation|keyboardHidden"

examples/Cpp/ExampleBase/ExampleBase.cpp

@@ -29,6 +29,7 @@
 
 #ifdef LLGL_OS_ANDROID
 #   include "Android/AppUtils.h"
+#   include <android/native_activity.h>
 #endif
 
 #define IMMEDIATE_SUBMIT_CMDBUFFER 0
@@ -386,6 +387,11 @@ void ExampleBase::Run()
     while (LLGL::Surface::ProcessEvents() && !window.HasQuit() && !input.KeyDown(LLGL::Key::Escape))
     #endif
     {
+        #ifdef LLGL_OS_ANDROID
+        if (input.KeyDown(LLGL::Key::BrowserBack))
+            ANativeActivity_finish(ExampleBase::androidApp_->activity);
+        #endif
+
         // Update profiler (if debugging is enabled)
         if (debuggerObj_)
         {