Dui reveal all items under label

[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

Reviewers
@vmoyseenko, please take a look.
I think yes, because class can contain not only methods, but also other classes... I'm talking about nested classes.