Add popupKeyboardTemplate attribute to Keyboard

This change
- introduces the popupKeyboardTemplate attribute of Keyboard to
  specify XML Keyboard file for popup mini keyboard.
- introduces the maxPopupKeyboardColumn attribute of Keyboard to
  specify the maximum column of popup mini keyboard.
- changes the content format of the popupCharacters attribute of Key.
  It now represents keyLabel, codes and keyTextOutput of each key of
  popup mini keyboard using CSV format.

Bug: 2214959
Change-Id: I539e310f7e38a049ee193de0b4ad5d7afdce37b1
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 47b3b45..3b20298 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -34,7 +34,7 @@
             android:key="popup_on"
             android:title="@string/popup_on_keypress"
             android:persistent="true"
-            android:defaultValue="@bool/default_popup_preview"
+            android:defaultValue="@bool/config_default_popup_preview"
             />
 
     <CheckBoxPreference