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.
@Benglin, I have tried the way introduced in `MapLogicalToVisualLineIndices`. But this one doesn't work. Created default `FontFamily`, not that one we are expecting for. My way is working. I have checked it. But I agree it doesn't look like an ideal solution.

[MSDN](http://msdn.microsoft.com/en-us/library/ms753303(v=vs.100).aspx) (at the bottom of page) says we can't use `pack` for referring to `FontFamily` in code.

Answering on second part of your message. We do not have access to `TextBlock` from `SearchViewModel` by design. One of solution to specify `RegularTypeFace` I see is to determine in `LibrarySearchView.xaml.cs` or in our converter.