Remove dotted black rectangle on selected listbox item

#### Purpose

We have next border for selected item in two listboxes. This PR removes it.
![dottedclass](https://cloud.githubusercontent.com/assets/8158551/4704848/95bef156-5875-11e4-88ca-8094c317be1f.PNG)
![dottedmember](https://cloud.githubusercontent.com/assets/8158551/4704847/95bc81d2-5875-11e4-9240-4192705e6489.PNG)

#### Modifications

Add `<Setter Property="FocusVisualStyle" Value="{x:Null}" />` for `ListBoxItem` style.

#### Additional references

[MAGN-5116](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5116).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.