Add memory store and error metrics in BW estimator

1) Add memory store support based on SharedPreferences and also add factory
reset.
2) Add estimation error metrics.
3) Refactor to remove LocalAreaNetworkBandwidth and
lookupLocalAreaNetwork().
4) Decouple from CarrierConfigManager or DcTracker by maintaining its
own per-RAT average BW table.
5) Move the fall-back-to-carrier-BW part to DataConnection.

Test: manual
Test: FrameworksTelephonyTests:com.android.internal.telephony
Bug: 176814680

Change-Id: I29a3101e3a805977e080e3cef7f36079acdb5b63