preferences: add donation link

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/preference/DonatePreference.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright © 2019 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.preference;
+
+import android.content.ActivityNotFoundException;
+import android.content.Context;
+import android.content.Intent;
+import android.net.Uri;
+import android.util.AttributeSet;
+
+import com.wireguard.android.Application;
+import com.wireguard.android.BuildConfig;
+import com.wireguard.android.R;
+
+import java.util.Locale;
+
+import androidx.annotation.Nullable;
+import androidx.preference.Preference;
+
+public class DonatePreference extends Preference {
+    public DonatePreference(final Context context, final AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    @Override
+    public CharSequence getSummary() { return getContext().getString(R.string.donate_summary); }
+
+    @Override
+    public CharSequence getTitle() { return getContext().getString(R.string.donate_title); }
+
+    @Override
+    protected void onClick() {
+        final Intent intent = new Intent(Intent.ACTION_VIEW);
+        intent.setData(Uri.parse("https://www.wireguard.com/donations/"));
+        try {
+            getContext().startActivity(intent);
+        } catch (final ActivityNotFoundException ignored) {
+        }
+    }
+
+}

app/src/main/res/values/strings.xml

@@ -66,6 +66,8 @@
     <string name="dark_theme_title">Use dark theme</string>
     <string name="delete">Delete</string>
     <string name="deselect_all">Deselect All</string>
+    <string name="donate_title">♥ Donate to the WireGuard Project</string>
+    <string name="donate_summary">Every contribution helps.</string>
     <string name="dns_servers">DNS servers</string>
     <string name="edit">Edit</string>
     <string name="endpoint">Endpoint</string>

app/src/main/res/xml/preferences.xml

@@ -15,4 +15,5 @@
         android:summaryOff="@string/dark_theme_summary_off"
         android:summaryOn="@string/dark_theme_summary_on"
         android:title="@string/dark_theme_title" />
+    <com.wireguard.android.preference.DonatePreference />
 </androidx.preference.PreferenceScreen>