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
I see, with the help of [this article on StackOverflow](http://stackoverflow.com/questions/10243327/how-raisepropertychangedt-finds-out-the-property-name), I now see that the statement raise property change that is equivalent for this:

```csharp
RaisePropertyChanged("SearchRootCategories");
```

Is that right? If that's the case, then is there a reason we stop hard-coding the name ```SearchRootCategories``` now? Because it seems *not the same as others* (I don't mean that's a bad thing).