* #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/loaders/HistoryLoader.java b/src/org/sflphone/loaders/HistoryLoader.java
index 22810b8..d3432a7 100644
--- a/src/org/sflphone/loaders/HistoryLoader.java
+++ b/src/org/sflphone/loaders/HistoryLoader.java
@@ -31,10 +31,10 @@
 
 package org.sflphone.loaders;
 
-import android.content.AsyncTaskLoader;
 import android.content.Context;
 import android.database.Cursor;
 import android.provider.ContactsContract;
+import android.support.v4.content.AsyncTaskLoader;
 import org.sflphone.history.HistoryCall;
 import org.sflphone.history.HistoryEntry;
 import org.sflphone.history.HistoryManager;