Dui key navigation(from cat to top to search)

Yellow navigation is from [first PR](https://github.com/Benglin/Dynamo/pull/123).
Pink is from [second PR](https://github.com/Benglin/Dynamo/pull/127).
Green is from [third PR](https://github.com/Benglin/Dynamo/pull/134).
Blue is from this one.
This PR makes navigation between categories, top result and search textbox possible.
![image](https://cloud.githubusercontent.com/assets/8158404/4732524/36b5dbf4-59bd-11e4-9b7e-d7da29db80d2.png)
Reviewers
@vmoyseenko, please take a look.

Link to YouTrack:
[MAGN-5074](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5074) DUI: Navigation should start from Top Result
As I remember `topResult.IsFocused` can't be `true` at this point. Please, remove it.