DUI: collapse class details

# Preface
Clicking on an expanded class icon should collapse the list. For example, clicking on the circle should collapse the list.
![image](https://cloud.githubusercontent.com/assets/8158404/4306076/f98ef3fa-3e7d-11e4-9fb3-15cad4bf79a2.png)
The classes that were opened should be closed when the category is closed.
For example. Open Geometry > Circle. Click on Builtin functions. Click on the Geometry again >> The circle class is open. It should be closed

# Reviewers
@Benglin,@vmoyseenko, please take a look.

Links to YouTrack:
[MAGN-4673](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4673) DUI: The classes that were opened should be closed when the category is closed.
[MAGN-4669](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4669) DUI: Clicking on an expanded class icon should collapse the list
Please rephrase the comment as follow:

```cs
// If user clicks on the same item when it is expanded, then 'OnClassButtonCollapse'
// is invoked to deselect the item. This causes 'OnClassViewSelectionChanged' to be 
// called again, with 'SelectedIndex' set to '-1', indicating that no item is selected,
// in which case we need to hide the standard panel.
```