Fix bug #15001610 Java crash in settings is observed while adding Google account on wiped device

- update Settings main layout to be able to show the Buttons
- make WifiPickerActivity a SettingsActivity and remove dead code
- fix reference to Buttons for using the Settings IDs instead
of the Framework ones

Change-Id: I23bfd1b8290fc007e6e80aa9a6297e55e7f6004e

res/layout/settings_main.xml

@@ -24,8 +24,9 @@
 
     <LinearLayout
             android:orientation="vertical"
-            android:layout_height="match_parent"
-            android:layout_width="match_parent">
+            android:layout_height="0px"
+            android:layout_width="match_parent"
+            android:layout_weight="1">
 
         <com.android.settings.widget.SwitchBar android:id="@+id/switch_bar"
                   android:layout_height="?android:attr/actionBarSize"
@@ -37,7 +38,6 @@
                 android:id="@+id/prefs"
                 android:layout_width="match_parent"
                 android:layout_height="match_parent"
-                android:layout_weight="1"
                 />
 
     </LinearLayout>