ProfileActivity: Refactor into clean layers of functionality

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

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

@@ -1,18 +0,0 @@
-package com.wireguard.android;
-
-import android.app.Fragment;
-import android.os.Bundle;
-import android.view.LayoutInflater;
-import android.view.View;
-import android.view.ViewGroup;
-
-/**
- * Fragment containing a simple placeholder message.
- */
-
-public class PlaceholderFragment extends Fragment {
-    @Override
-    public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
-        return inflater.inflate(R.layout.placeholder_fragment, parent, false);
-    }
-}