Refactor hotspot into a full page

- Deprecated WifiAPEnabler, and copied most of its logic into various
  controllers and WifiTetherSettings.
- Added tests

Fix: 37253404
Fix: 36181835

Test: make RunSettingsRoboTests
Change-Id: Iad994d61b694ad7f1113d045a3e7500eeaec178b

src/com/android/settings/wifi/WifiApEnabler.java

@@ -32,6 +32,10 @@ import com.android.settings.datausage.DataSaverBackend;
 
 import java.util.ArrayList;
 
+/**
+ * @deprecated in favor of WifiTetherPreferenceController and WifiTetherSettings
+ */
+@Deprecated
 public class WifiApEnabler {
     private final Context mContext;
     private final SwitchPreference mSwitch;