Enable proxy to subscription manager in data usage UI.
Bug: 141833767
Test: manual
make RunSettingsRoboTests -j ROBOTEST_FILTER=BillingCyclePreferenceTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=CellDataPreferenceTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageListTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageSummaryTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageUtilsTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=MobileDataEnabledListenerTest
Change-Id: Id119738dc16ece8767c088b9a0794997e4b0334f
1. Create a singleton to reduce number of SubscriptionManager accessing
2. Listening to Airplane mode change to clear cache value
Bug: 141833767
Test: Manual
make RunSettingsRoboTests -j ROBOTEST_FILTER=MobileNetworkActivityTest
make RunSettingsRoboTests -j ROBOTEST_FILTER=GlobalSettingsChangeListenerTest
Change-Id: Icd76fd9bcef7a7822400bfe42b0d40f5bd920eed