Wpf

I fixed a couple of the scenarios you had.

```ruby
on(WpfGrid).parts = some_value
```
This does not work because in UISpy if you look at the `dataitem` children for the grid, it is _their_ value that is considered for that. In this control, it looks like they're all the same. Therefore you have to resort to the `:select_` / `:find_` methods for this control.