Add keyHintIcon attribute to BaseKeyboard.Key class

This keyHintIcon attribute is used to specify hint icon drawable at
top right corner of Key.

Change-Id: Icaa91e63c4473b2513396bd3fbeb8ed6fd73586c
diff --git a/java/res/values/strings.xml b/java/res/values/strings.xml
index 94fe76d..a05d291 100644
--- a/java/res/values/strings.xml
+++ b/java/res/values/strings.xml
@@ -212,6 +212,8 @@
     <string name="label_alpha_key">ABC</string>
     <!-- Label for ALT modifier key.  Must be short to fit on key! -->
     <string name="label_alt_key">ALT</string>
+    <!-- Label for Shift modifier key of symbol keyboard.  Must be short to fit on key! -->
+    <string name="label_more_key">More</string>
 
     <!-- Voice related labels -->