Highlight of search phrase in member name

#### Purpose

Highlight search phrase in member name. Proposed design is on screenshot.
![highlight1](https://cloud.githubusercontent.com/assets/8158551/4780809/5d064be0-5c79-11e4-8df8-359d1581aac8.PNG)

#### Modifications

Added `Rectangle` near each member's `TextBlock`. Created converter `SearchHighlightMarginConverter` which returns correct `Margin` for just added `Rectangle`.

#### Additional references

[MAGN-4916](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4916).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.
Is it possible to move this ```10``` and ```5``` outside of the ```Margin``` computation? It seems odd to have to add these numbers here to make a ```Thickness``` object. Can we try the following (i.e. move these magic numbers out to ```Border``` element to make some fixed spacing):

```xml
<Grid>
    <Border Padding="5,10,5,10">
        <Rectangle>
            <Rectangle.Margin>
                <MultiBinding ... />
            </Rectangle.Margin>
        </Rectangle>
    </Border>
</Grid>
```