Refactor KeyboardTheme

This CL introduces two preference keys in addition to the existing one.

- pref_keyboard_theme: The new preference key that is used only in the
  preference settings.

- pref_keyboard_layout_20110916: The previous preference key that
  holds keyboard color scheme settings. This is superseded by the next
  key.

- pref_keyboard_theme_20140509: The new preference key that holds
  keyboard theme settings. This value is forcibly reset to LMP theme
  on a LMP device. On a KitKat and previous device, the settings of
  the pref_keyboard_layout_20110916 is carried on into this
  preference.

This CL must be checked in together with Id7b3ddd8aa.

Change-Id: I2d55602d026e30b38d8f822d2124f5c5e4a9a812
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 7d86dbd..61ebb69 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -158,12 +158,11 @@
                 android:persistent="true"
                 android:defaultValue="false" />
             <ListPreference
-                android:key="pref_keyboard_layout_20110916"
+                android:key="pref_keyboard_theme"
                 android:title="@string/keyboard_color_scheme"
                 android:persistent="true"
                 android:entryValues="@array/keyboard_theme_ids"
-                android:entries="@array/keyboard_theme_names"
-                android:defaultValue="@string/config_default_keyboard_theme_id" />
+                android:entries="@array/keyboard_theme_names" />
             <PreferenceScreen
                 android:fragment="com.android.inputmethod.latin.settings.AdditionalSubtypeSettings"
                 android:key="custom_input_styles"