* #39101: revert to compatibility fragments

There is an issue in a UI element (ViewPager), which does not get properly populated
when restoring its state. (found using VMs with API=16)
diff --git a/src/org/sflphone/fragments/DropActionsChoice.java b/src/org/sflphone/fragments/DropActionsChoice.java
index e181304..a97064b 100644
--- a/src/org/sflphone/fragments/DropActionsChoice.java
+++ b/src/org/sflphone/fragments/DropActionsChoice.java
@@ -31,6 +31,7 @@
 
 package org.sflphone.fragments;
 
+import android.support.v4.app.DialogFragment;
 import org.sflphone.R;
 
 import android.app.AlertDialog;
@@ -38,7 +39,6 @@
 import android.content.DialogInterface;
 import android.content.Intent;
 import android.os.Bundle;
-import android.app.DialogFragment;
 import android.view.View;
 import android.widget.AdapterView;
 import android.widget.AdapterView.OnItemClickListener;