Added about activity.

src/main/java/de/dennisguse/opentracks/AboutActivity.java

@@ -0,0 +1,37 @@
+package de.dennisguse.opentracks;
+
+import android.os.Bundle;
+import android.view.Menu;
+import android.widget.TextView;
+
+import androidx.annotation.Nullable;
+
+import de.dennisguse.opentracks.util.SystemUtils;
+
+public class AboutActivity extends AbstractActivity {
+
+    @Override
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        setTitle(getString(R.string.about_preference_title));
+
+        TextView textDescription = findViewById(R.id.about_text_description);
+        textDescription.setText(getString(R.string.about_description));
+
+        TextView textVersion = findViewById(R.id.about_text_version);
+        textVersion.setText(getString(R.string.about_version, SystemUtils.getAppVersion(this)));
+
+        TextView textURL = findViewById(R.id.about_app_url);
+        textURL.setText(getString(R.string.about_url, getString(R.string.app_web_url)));
+    }
+
+    protected int getLayoutResId() {
+        return R.layout.about;
+    }
+
+    @Override
+    public boolean onCreateOptionsMenu(Menu menu) {
+        return false;
+    }
+}

src/main/java/de/dennisguse/opentracks/util/IntentUtils.java

@@ -36,8 +36,6 @@ import java.io.File;
  */
 public class IntentUtils {
 
-    public static final String TEXT_PLAIN_TYPE = "text/plain";
-
     private IntentUtils() {
     }