Unit tests for ShortenCategoryName

#### Purpose

Write unit tests for function `SearchViewModel.ShortenCategoryName`.

#### modifications

Test function is added. Screenshot of results:
![image](https://cloud.githubusercontent.com/assets/8158551/4736511/1749a5f4-59ed-11e4-8cef-9fa03c879c6d.png)

#### Additional references

[MAGN-4939](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4939).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.