Scroll bar in documentation tree

[Jörg Pauly]

Hello, everyone.

I saw that there's no scroll bar in the documentation tree view. This is not 
really nice, if you have a lot of doc packages registered.

I think, this should be added.

Is someone already caring for it? Otherwise I could have a look; if maybe 
someone could give me a little tip where to start to look for it.

Kind regards
Joerg Pauly