* #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/CallListFragment.java b/src/org/sflphone/fragments/CallListFragment.java
index 6a9b628..9aae4b2 100644
--- a/src/org/sflphone/fragments/CallListFragment.java
+++ b/src/org/sflphone/fragments/CallListFragment.java
@@ -31,7 +31,6 @@
 package org.sflphone.fragments;
 
 import android.app.Activity;
-import android.app.Fragment;
 import android.content.ClipData;
 import android.content.ClipData.Item;
 import android.content.Context;
@@ -39,6 +38,7 @@
 import android.content.IntentFilter;
 import android.graphics.Color;
 import android.os.*;
+import android.support.v4.app.Fragment;
 import android.util.Log;
 import android.view.DragEvent;
 import android.view.LayoutInflater;