add FileChooser

app/src/main/java/de/joel/zoomhelper/FileChooser.java

@@ -0,0 +1,22 @@
+package de.joel.zoomhelper;
+
+import android.app.Activity;
+import android.content.Intent;
+
+import java.io.File;
+
+public class FileChooser {
+    // Request code for selecting a PDF document.
+    private final Activity act;
+
+    public FileChooser (Activity act) {
+        this.act = act;
+    }
+
+    public void openFile() {
+        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
+        intent.addCategory(Intent.CATEGORY_OPENABLE);
+        intent.setType("application/octet-stream");
+        act.startActivityForResult(intent, 2);
+    }
+}