Add activity for mobile network page

1. Extract the Tabhost to activity level, not fragment level. So
each mobile fragment has a constant subscriptionId
2. Use BottomNavigationView instead of TabHost

Bug: 114749736
Test: RunSettingsRoboTests
Change-Id: I43aebf2ec01a945697c6b2302ab750e715e4bfef
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 94be61c..386c99c 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -131,6 +131,13 @@
                   android:launchMode="singleTask">
         </activity>
 
+        <activity android:name=".mobilenetwork.MobileSettingsActivity"
+                  android:label="@string/network_settings_title"
+                  android:theme="@style/Theme.Settings.Home"
+                  android:launchMode="singleTask">
+            <!-- TODO(b/114749736): add intent filter here and disable the one in telephony -->
+        </activity>
+
         <!-- Alias for launcher activity only, as this belongs to each profile. -->
         <activity-alias android:name="Settings"
                 android:taskAffinity="com.android.settings.root"