Android: Add simple launcher

This adds a minimal launcher activity for the android app, which does
the followings:

- Opens a file chooser to let user select a zip file
- Extracts the zip into the app's internal storage
- Launches the SDL activity

android/app/src/main/java/io/github/kichikuou/system3/GameActivity.java

@@ -0,0 +1,35 @@
+/* Copyright (C) 2019 <KichikuouChrome@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+*/
+package io.github.kichikuou.system3;
+
+import org.libsdl.app.SDLActivity;
+
+public class GameActivity extends SDLActivity {
+    @Override
+    protected String[] getLibraries() {
+        return new String[] {
+            "hidapi",
+            "SDL2",
+            // "SDL2_image",
+            // "SDL2_mixer",
+            // "SDL2_net",
+            // "SDL2_ttf",
+            "system3"
+        };
+    }
+}

android/app/src/main/java/io/github/kichikuou/system3/LauncherActivity.java

@@ -0,0 +1,91 @@
+/* Copyright (C) 2019 <KichikuouChrome@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+*/
+package io.github.kichikuou.system3;
+
+import android.app.Activity;
+import android.content.Intent;
+import android.net.Uri;
+import android.os.Build;
+import android.os.Bundle;
+import android.util.Log;
+
+import java.io.BufferedInputStream;
+import java.io.BufferedOutputStream;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.Charset;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+
+public class LauncherActivity extends Activity {
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        Intent i = new Intent(Intent.ACTION_GET_CONTENT);
+        i.setType("application/zip");
+        startActivityForResult(Intent.createChooser(i, "Choose a file"), 0);
+    }
+
+    @Override
+    public void onActivityResult(int requestCode, int resultCode, Intent data) {
+        if (resultCode == RESULT_OK)
+            extractFiles(data.getData(), getApplicationContext().getFilesDir());
+        startGame();
+    }
+
+    boolean extractFiles(Uri zipUri, File outDir) {
+        try {
+            InputStream input = getContentResolver().openInputStream(zipUri);
+            if (input == null)
+                return false;
+            ZipInputStream zip;
+            if (Build.VERSION.SDK_INT >= 24)
+                zip = new ZipInputStream(new BufferedInputStream(input), Charset.forName("Shift_JIS"));
+            else
+                zip = new ZipInputStream(new BufferedInputStream(input));
+            byte[] buffer = new byte[4096];
+            ZipEntry zipEntry;
+            while ((zipEntry = zip.getNextEntry()) != null) {
+                File entryName = new File(zipEntry.getName());
+                if (zipEntry.isDirectory())
+                    continue;
+                Log.d("Extracting", entryName.toString());
+                File outFile = new File(outDir, entryName.getName());
+                BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream(outFile));
+                int size;
+                while ((size = zip.read(buffer)) > 0) {
+                    output.write(buffer, 0, size);
+                }
+                output.close();
+            }
+            zip.close();
+            return true;
+        } catch (IOException e) {
+            Log.e("launcher", "Error while extracting zip", e);
+            return false;
+        }
+    }
+
+    void startGame() {
+        Intent i = new Intent();
+        i.setClass(getApplicationContext(), GameActivity.class);
+        startActivity(i);
+    }
+}