DUI: reveal all items under label

State: _High_
# Preface
All members should appear after click on Group. Group should be highlighted, when mouse is over, and underlined after selection.
# Before
![image](https://cloud.githubusercontent.com/assets/8158404/4766417/3292b09e-5b50-11e4-9ffb-122c9360622d.png)
# After
![image](https://cloud.githubusercontent.com/assets/8158404/4766420/3df10d3c-5b50-11e4-8c98-40e41cee4690.png)
# Reviewers
@Benglin ,@vmoyseenko, please take a look.

Link to YouTrack:
[MAGN-4919](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4919) DUI: On clicking each of the labels of results, they should reveal all items under that label
Unfortunately the comment here is for ```GroupName```, not ```Prefix```, we need that updated to avoid creating confusion.