Added right side icons for addon root category

#### Purpose

Add library type and update icons to addon top category.

#### Modifications

Looks like it. I have made some cheating in logic to make this view. Just to get the meaning of task. 
![image](https://cloud.githubusercontent.com/assets/8158551/5032693/82242c28-6b68-11e4-82c7-885a84b66dc7.png)

Created two properties in `BrowserRootElement` to control new icons. Added XAML and binding. Need to implement logic of getters / setters. Will be done in another PR.

#### Additional references

[MAGN-4650](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4650).
[MAGN-4652](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4652).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.

@elayabharath, do you like an update icon? if no please provide correct version of it.
Rename this to ```ElementTypeToShorthandConverter```.