SettingsActivity: Implement primary config setting

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

app/src/main/java/com/wireguard/android/SettingsActivity.java

@@ -1,6 +1,23 @@
 package com.wireguard.android;
 
 import android.app.Activity;
+import android.app.FragmentTransaction;
+import android.os.Bundle;
+import android.preference.PreferenceFragment;
 
 public class SettingsActivity extends Activity {
+    @Override
+    protected void onCreate(final Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        final FragmentTransaction transaction = getFragmentManager().beginTransaction();
+        transaction.replace(android.R.id.content, new SettingsFragment()).commit();
+    }
+
+    public static class SettingsFragment extends PreferenceFragment {
+        @Override
+        public void onCreate(final Bundle savedInstanceState) {
+            super.onCreate(savedInstanceState);
+            addPreferencesFromResource(R.xml.preferences);
+        }
+    }
 }

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

@@ -20,6 +20,8 @@
     <string name="listen_port">Listen port</string>
     <string name="mtu">MTU</string>
     <string name="placeholder_text">No configuration selected</string>
+    <string name="primary_config">Primary configuration</string>
+    <string name="primary_config_summary">This configuration will be controlled by the quick settings tile</string>
     <string name="private_key">Private key</string>
     <string name="public_key">Public key</string>
     <string name="save">Save</string>

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

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <com.wireguard.android.ConfigListPreference
+        android:key="primary_config"
+        android:summary="@string/primary_config_summary"
+        android:title="@string/primary_config" />
+</PreferenceScreen>