Create groupIndicator for ExpandableListView example

Modify from last exercise "ExpandableListView example", to create groupIndicator.

Copy drawables to /res/drawable/ folder. In my exercise, btn_check_buttonless_on.png and btn_check_buttonless_off.png copied from Android SDK folder: /Android/sdk/platforms/android-20/data/res/drawable-mdpi/

Create /res/drawable/groupindicator.xml, to define our groupIndicator.

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/btn_check_buttonless_off"
       android:state_expanded="true" />
   <item android:drawable="@drawable/btn_check_buttonless_on"/>
</selector>

Modify /res/layout/activity_main.xml to specify android:groupIndicator of ExpandableListView.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.androidexpandablelistview.MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />

    <ExpandableListView
        android:id="@+id/mylist"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:groupIndicator="@drawable/groupindicator" />

</LinearLayout>

Next:
- Place groupIndicator of ExpandableListView on right side