title: How open not main activity from Notification
body: <p>In my app I have a Activity that is opened from a Notification, but is not declared has main activity or launcher activity·
  Also, this activity is declared has "singleTop".
  Works fine for most users, but some are a little problem.
  In some occassions when click the Notification the Activity is opened and, when click back, the app Main Activity is shown. 
  How to don't show the main activity when click back?
  Also, if the users are in this activity and click home, and later it clicks into the app icon in order to open the Main activity, the previously opened activity, that is not main activity is opened. This can change?
  Thanks.</p>
  
  <p>-- The structure of the manifest is:</p>
  
  <pre><code>    &lt;activity android:name=".MainActivity" android:label="@string/app_name" android:exported="true" android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.MAIN" /&gt;
              &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;  
  
  
      &lt;activity android:name=".ShowAlarmsActivity" android:launchMode="singleTop" android:exported="true" android:theme="@style/AppThemeWithoutActionBar" /&gt;
  </code></pre>