Add ability to show/hide Wi-Fi settings, and all related sub-settings.

This adds a new boolean flag, config_show_wifi_settings, which when set
to false will hide the "Wi-Fi" page in network & internet (there is no
key value associated with this preference page). It will also hide
nested pages from search results, such as Wi-Fi preferences.

Bug: 62379554
Test: make RunSettingsRoboTests
ROBOTEST_FILTER=ConfigureWifiSettingsTest
and
make RunSettingsRoboTests
ROBOTEST_FILTER=WifiSettingsTest
and
make RunSettingsRoboTests
ROBOTEST_FILTER=WifiMasterSwitchPreferenceControllerTest
all pass.

Change-Id: Iedc6bc272e0cb2b561c6bf25968e70f355aaaa8e

tests/robotests/src/com/android/settings/wifi/WifiMasterSwitchPreferenceControllerTest.java

@@ -72,10 +72,17 @@ public class WifiMasterSwitchPreferenceControllerTest {
     }
 
     @Test
-    public void isAvailable_shouldAlwaysReturnTrue() {
+    public void testWifiMasterSwitch_byDefault_shouldBeShown() {
         assertThat(mController.isAvailable()).isTrue();
     }
 
+    @Test
+    @Config(qualifiers = "mcc999")
+    public void testWifiMasterSwitch_ifDisabled_shouldNotBeShown() {
+        assertThat(mController.isAvailable()).isFalse();
+    }
+
+
     @Test
     public void onResume_shouldRegisterCallback() {
         mController.onResume();