ProfileList: Extract service management into a base class

It will be shared with other fragments.

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

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

@@ -0,0 +1,37 @@
+package com.wireguard.android;
+
+import android.app.Fragment;
+import android.content.Context;
+
+/**
+ * Base class for fragments that are part of a ProfileActivity.
+ */
+
+public class ProfileActivityFragment extends Fragment implements ServiceConnectionListener {
+    private ProfileActivity activity;
+    protected ProfileServiceInterface service;
+
+    @Override
+    public void onAttach(Context context) {
+        super.onAttach(context);
+        activity = (ProfileActivity) context;
+        activity.addServiceConnectionListener(this);
+        service = activity.getService();
+    }
+
+    @Override
+    public void onDetach() {
+        super.onDetach();
+        activity.removeServiceConnectionListener(this);
+    }
+
+    @Override
+    public void onServiceConnected(ProfileServiceInterface service) {
+        this.service = service;
+    }
+
+    @Override
+    public void onServiceDisconnected() {
+        service = null;
+    }
+}