DUI: Regular nodes and addons is sorted in alphabetical order.

Alphabetical order was created for:
1. Top categories.
2. Addons treeview.
3. Top search categories.
4. Members in top search categories.

Only one thing troubles me.
If we make alphabetical order for search members, first member is always top result... It seams like reduplication, not like top result.
![image](https://cloud.githubusercontent.com/assets/8158404/4917675/d4dc8bf4-64e7-11e4-8967-0b43bccc1cd7.png)
![image](https://cloud.githubusercontent.com/assets/8158404/4917680/e49dfb40-64e7-11e4-9da6-612e0167b725.png)

Reviewers
@Benglin ,@vmoyseenko, please take a look.
@elayabharath, I think you need to look through too.

Link to YouTrack:
[MAGN-5270](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5270) DUI: Regular nodes and addons should be sorted in alphabetical order
Firstly I wrote `RaisePropertyChanged("Model");` and this statement refreshes the whole model. As I understand `() => Model.SearchRootCategories` refreshes only `SearchRootCategories` property...