Update settings for app hibernation

Created an preference in Apps & Notifcations page as the entry point for
apps that are hibernated. Also added a switch preference in AppInfo page
for users to exempt an app from hibernation.

Bug: 181172051
Test: HibernatedAppsPreferenceControllerTest;
HibernationSwitchPreferenceControllerTest;
AppInfoDashboardFragmentTest

Change-Id: I72a90ab391cd521150fc155a6d9c67c846b7360d
diff --git a/src/com/android/settings/Utils.java b/src/com/android/settings/Utils.java
index e44ee78..4bf97cc 100644
--- a/src/com/android/settings/Utils.java
+++ b/src/com/android/settings/Utils.java
@@ -153,6 +153,9 @@
     public static final String PROPERTY_LOCATION_INDICATOR_SETTINGS_ENABLED =
             "location_indicator_settings_enabled";
 
+    /** Whether or not app hibernation is enabled on the device **/
+    public static final String PROPERTY_APP_HIBERNATION_ENABLED = "app_hibernation_enabled";
+
     /**
      * Finds a matching activity for a preference's intent. If a matching
      * activity is not found, it will remove the preference.