DUI: Nested structure prototype. (don't merge)

# Preface
 The nested namespaces will be shown as expandable list until the classes are found. 
![image](https://cloud.githubusercontent.com/assets/8158404/4405870/dc2cfe1e-44be-11e4-985a-ef87700106d3.png)

# Solution
As it was discussed. I changed main `Listview` to `Treeview`. Also, I've added `NestedClassesTemplate`.

# Before
![image](https://cloud.githubusercontent.com/assets/8158404/4406042/010a4f88-44c0-11e4-8bd4-8c00aab380e3.png)
# After
![image](https://cloud.githubusercontent.com/assets/8158404/4405956/6159b596-44bf-11e4-8a80-d7fa361b5507.png)

# Reviewers
@Benglin,@vmoyseenko, please take a look.
Please, move this `TemplateSelector` near to his `DataTemplates`. To line 312 - 313, for example.