Change start page's samples list box to treeView

Added show samples in folder
![capture](https://cloud.githubusercontent.com/assets/8348435/4116505/c1009dda-3285-11e4-8b33-550f9b37465a.PNG)

Hi @theanh0512, we should improve the XAML for better readability. Do the following to change this:

1. Go to ```Options``` in Visual Studio
2. ```Text Editor``` > ```XAML``` > ```Formatting``` > ```Spacing```
3. Select ```Position each attribute on a separate line```
4. Select ```Position the first attribute on the same line as start tag```

Then do the following each time you submit a XAML file:

1. Select **only** the XAML part you have updated
2. Press ```CTRL+E+F``` to format your selection

Then all your updated XAML tags will line up properly (**do not** do that for the entire file).