Top Result for LibrarySearchView

#### Purpose

Add Top Result to UI. Style it.
![top_result](https://cloud.githubusercontent.com/assets/8158551/4588825/a438f00c-504a-11e4-8b71-12d739105939.PNG)

#### Modifications

Member UI moved to `ControlTemplate`. Created `SearchViewModel.TopResult` variable. 

#### Additional references

[MAGN-4911](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4911).
[MAGN-4912](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4912) done partially. Pressing Enter not create node. Will be done in other PR.

Also Top Result is not selected by default - there is simple changed background. Task for it: [MAGN-5008](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5008).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.
I see, in this case let's leave it as a ```ListBox``` then, that will avoid unnecessary code changes that we need in order to turn this into a ```StackPanel```, which will be maintenance problem, too. So this looks good!