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.
Thanks a lot for your work, @vmoyseenko. This looks awesome and I can't wait to see it in action! I do have some concerns about performance and as my usual self, I always like to see if there is a better way to do things. So here's what I think...

Instead of just ```DataContext.SearchText```, is it possible to pass the entire ```DataContext``` (i.e. ```LibrarySearchView```) to ```SearchHighlightMarginConverter```? The reason I ask is because I would like to find a way to cache ```Typeface```, it should be created only once in ```LibrarySearchView``` and kept for use repeatedly in ```FormattedText```.