title: add action bar with back button in preference activity
body: <p>Here is my preference activity:</p>
  
  <pre><code>package com.example.hms.test;
  
  import android.os.Bundle;
  import android.preference.PreferenceActivity;
  
  public class PrefsActivity extends PreferenceActivity {
  
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          addPreferencesFromResource(R.xml.prefs);
      }
  
  }
  </code></pre>
  
  <p>here I want to show an actionbar with name settings and a back button to home</p>