Show/Hide/Change appropriate buttons in footer of MessageList.

BUG: 1904403

* Change the text of READ/UNREAD button dynamically according to the state of selection
* Change the text of favorite button dynamically according to the state of selection
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 7443fb2..c3b00e4 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -57,7 +57,15 @@
     <!-- Menu item/button name -->
     <string name="read_unread_action">Read/Unread</string>
     <!-- Menu item/button name -->
+    <string name="read_action">Mark Read</string>
+    <!-- Menu item/button name -->
+    <string name="unread_action">Mark Unread</string>
+    <!-- Menu item/button name -->
     <string name="favorite_action">Favorite</string>
+    <!-- Menu item/button name -->
+    <string name="set_star_action">Mark Star</string>
+    <!-- Menu item/button name -->
+    <string name="remove_star_action">Remove Star</string>
     <!-- Menu item -->
     <string name="refresh_action">Refresh</string>
     <!-- Menu item -->