DUI: key navigation(prototype)

It's just start of new focus navigation. I left a lot of comments in code to make it as clear as possible. Next week I will continue, but I need to know: have I chosen the right way of implementation?
Thank you in advance.

Reviewers:
@Benglin,@vmoyseenko, please take a look.

Tasks on YouTrack:
[MAGN-4851](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4851) DUI: Add arrow keys navigation for selecting each of the items under lists