Update Android java code (#7820)

Targets SDK 26 as required by the playstore.
Fixes screen auto-rotation closing game.
Hides on-screen navigation bar if present.

Update gradlew.
Fix display aspect on 18+/:9 displays (like a Samsung Galaxy S9).
Remove small app icons, not required.
Fix xml in unpacking activity.
Support Android permission: On Android 6.0+ you need to manually give write
permission (as required by google).
Background during unpacking (just a demo for now).
Material Design: no more Android 2 interface.
Immersive mode (Android 4.4+ - hide NavBar for fullscreen mode).

build/android/src/main/res/drawable/bg.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
+	android:src="@drawable/background"
+	android:tileMode="repeat" />

build/android/src/main/res/layout/assetcopy.xml

@@ -1,24 +1,24 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    android:layout_width="fill_parent"
-    android:layout_height="fill_parent"
-    android:orientation="vertical" >
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	android:id="@+id/activity_main"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent">
 
-    <ProgressBar
-        android:id="@+id/progressBar1"
-        style="?android:attr/progressBarStyleHorizontal"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:layout_gravity="center_vertical" />
+	<ProgressBar
+		android:id="@+id/progressBar1"
+		style="?android:attr/progressBarStyleHorizontal"
+		android:layout_width="match_parent"
+		android:layout_height="30dp"
+		android:layout_centerInParent="true"
+		android:layout_marginLeft="90dp"
+		android:layout_marginRight="90dp" />
 
-    <TextView
-        android:id="@+id/textView1"
-        android:layout_width="match_parent"
-        android:layout_height="wrap_content"
-        android:ellipsize="middle" 
-        android:singleLine="true"
-        android:layout_gravity="center_horizontal"
-        android:text="@string/preparing_media"
-        android:textAppearance="?android:attr/textAppearanceSmall" />
+	<TextView
+		android:id="@+id/textView1"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:layout_below="@+id/progressBar1"
+		android:layout_centerInParent="true"
+		android:text="@string/preparing_media" />
 
-</LinearLayout>
+</RelativeLayout>

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

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+
+	<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>
+	</style>
+
+	<style name="Theme.Dialog" parent="@android:style/Theme.Material.Light.Dialog.NoActionBar"/>
+
+</resources>

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

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-	<string name="preparing_media">Preparing media...</string>
-</resources>
-
+	<string name="preparing_media">Preparing media&#8230;</string>
+	<string name="not_granted">Required permission wasn\'t granted, Minetest can\'t run without it</string>
+</resources>

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

@@ -1,11 +1,12 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-	<style name="Theme.Transparent" parent="android:Theme">
-		<item name="android:windowIsTranslucent">true</item>
-		<item name="android:windowBackground">@android:color/transparent</item>
-		<item name="android:windowContentOverlay">@null</item>
+
+	<style name="AppTheme" parent="@android:style/android:Theme.Holo.Light.NoActionBar.Fullscreen">
 		<item name="android:windowNoTitle">true</item>
-		<item name="android:windowIsFloating">true</item>
-		<item name="android:backgroundDimEnabled">false</item>
+		<item name="android:windowAnimationStyle">@null</item>
+		<item name="android:background">@drawable/bg</item>
 	</style>
+
+	<style name="Theme.Dialog" parent="@android:style/android:Theme.Holo.Light.Dialog.NoActionBar"/>
+
 </resources>