Introduce IconProvider.

Bug: 27506625

-Move managing of SystemState to IconProvider

Change-Id: I3417f0b7d0664c2255c7cc2a88f6c65822b5fb98
diff --git a/res/values/config.xml b/res/values/config.xml
index 90df997..8d69f9a 100644
--- a/res/values/config.xml
+++ b/res/values/config.xml
@@ -68,6 +68,9 @@
          filter the activities shown in the launcher. Can be empty. -->
     <string name="app_filter_class" translatable="false"></string>
 
+    <!-- Name of an icon provider class. -->
+    <string name="icon_provider_class" translatable="false"></string>
+
     <!-- View ID to use for QSB widget -->
     <item type="id" name="qsb_widget" />