added bigram prediction
  - after first character, only suggests bigram data (but doesn't autocomplete)
  - after second character, words from dictionary gets rearranged by using bigram
  - compatible with old dictionary
  - added preference option to disable bigram

Change-Id: Ia8f4e8fa55e797e86d858fd499887cd396388411
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 535b63f..c93fe0a 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -81,6 +81,14 @@
             android:defaultValue="@bool/enable_autocorrect"
             android:dependency="show_suggestions"
             />
-            
+
+        <CheckBoxPreference
+            android:key="bigram_suggestion"
+            android:title="@string/bigram_suggestion"
+            android:summary="@string/bigram_suggestion_summary"
+            android:persistent="true"
+            android:defaultValue="true"
+            android:dependency="auto_complete"
+            />
     </PreferenceCategory>            
 </PreferenceScreen>