Android: Fix start-up crashes on version 4.x (#8003)

* Android: Load shared STL library

* Android: Fix exception with window background image

build/android/src/main/java/net.minetest.minetest/MtNativeActivity.java

@@ -10,6 +10,7 @@
public class MtNativeActivity extends NativeActivity {

	static {
		System.loadLibrary("c++_shared");
		System.loadLibrary("openal");
		System.loadLibrary("ogg");
		System.loadLibrary("vorbis");

build/android/src/main/res/values-v21/styles.xml

@@ -4,9 +4,9 @@
	<style name="AppTheme" parent="@android:style/android:Theme.Material.Light.NoActionBar.Fullscreen">
		<item name="android:windowNoTitle">true</item>
		<item name="android:windowAnimationStyle">@null</item>
		<item name="android:background">@drawable/bg</item>
		<item name="android:windowBackground">@drawable/bg</item>
	</style>

	<style name="Theme.Dialog" parent="@android:style/Theme.Material.Light.Dialog.NoActionBar"/>

</resources>
</resources>

build/android/src/main/res/values/styles.xml

@@ -4,9 +4,9 @@
	<style name="AppTheme" parent="@android:style/android:Theme.Holo.Light.NoActionBar.Fullscreen">
		<item name="android:windowNoTitle">true</item>
		<item name="android:windowAnimationStyle">@null</item>
		<item name="android:background">@drawable/bg</item>
		<item name="android:windowBackground">@drawable/bg</item>
	</style>

	<style name="Theme.Dialog" parent="@android:style/android:Theme.Holo.Light.Dialog.NoActionBar"/>

</resources>
</resources>