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)

Add an internal method:

```cs
public class SampleFileEntry
{
    internal void AddChildEntry(SampleFileEntry entry)
    {
        childProperties.Add(entry);
    }
}
```