Use a ListView to store discovered child devices

The previous approach was to list buttons in a TableLayout.
However, this approach does not work well if there are more
items than can fit on the screen.

To allow scrolling of items, and also a better presentation
of said items, use a ListView.

res/layout/activity_discover.xml

@@ -29,12 +29,13 @@
         android:text="@string/selectChildDevice"
         android:textSize="20sp" />
 
-    <TableLayout
+    <ListView
         android:id="@+id/ServiceTable"
+        android:scrollbars="vertical"
         android:layout_width="match_parent"
-        android:layout_height="wrap_content"
+        android:layout_height="0dp"
         android:layout_weight="0.32"
         android:padding="10dp" >
-    </TableLayout>
+    </ListView>
 
 </LinearLayout>