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.
It is made as `ListBox` to reuse current data structure. We provide `SearchMemberGroup`. We can replace this `ListBox` to `StackPanel`. In this case we need to create Converter to get from `Members` collection first element or propose new class specially for `TopResult`. If any of this ways is more preferable, I will implement it.