Add donate links; via PayPal on full version or refer to website (that has a link) on lite version. Fixes #329.

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

@@ -18,4 +18,7 @@
 
 	<string name="app_name" translatable="false">Transdroid</string>
 
+	<string name="donate_text">Donate with PayPal</string>
+	<string name="donate_url">https://paypal.me/erickoknl</string>
+
 </resources>

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

@@ -18,4 +18,7 @@
 
 	<string name="app_name" translatable="false">Transdrone</string>
 
+	<string name="donate_text">Donate via transdroid.org</string>
+	<string name="donate_url">https://transdroid.org</string>
+
 </resources>

app/src/main/java/org/transdroid/core/gui/settings/MainSettingsActivity.java

@@ -23,6 +23,7 @@ import android.content.DialogInterface;
 import android.content.DialogInterface.OnClickListener;
 import android.content.Intent;
 import android.content.SharedPreferences;
+import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
 import android.preference.ListPreference;
@@ -113,6 +114,13 @@ public class MainSettingsActivity extends PreferenceCompatActivity {
 			return true;
 		}
 	};
+	private OnPreferenceClickListener onDonate = new OnPreferenceClickListener() {
+		@Override
+		public boolean onPreferenceClick(Preference preference) {
+			startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(getString(R.string.donate_url))));
+			return true;
+		}
+	};
 	private OnServerClickedListener onServerClicked = new OnServerClickedListener() {
 		@Override
 		public void onServerClicked(ServerSetting serverSetting) {
@@ -183,6 +191,7 @@ public class MainSettingsActivity extends PreferenceCompatActivity {
 		findPreference("header_background").setOnPreferenceClickListener(onBackgroundSettings);
 		findPreference("header_system").setOnPreferenceClickListener(onSystemSettings);
 		findPreference("header_help").setOnPreferenceClickListener(onHelpSettings);
+		findPreference("header_donate").setOnPreferenceClickListener(onDonate);
 
 		// Keep a list of the server codes and names (for default server selection)
 		List<String> serverCodes = new ArrayList<>();

app/src/main/res/xml/pref_main.xml

@@ -72,6 +72,10 @@
 			android:key="header_help"
 			android:title="@string/pref_help"
 			android:order="303" />
+		<Preference
+			android:key="header_donate"
+			android:title="@string/donate_text"
+			android:order="304" />
 	</PreferenceCategory>
 	
 </PreferenceScreen>