Filter Visual Studio solution explorer using GitHub Pull Request

Add possibility to filter Visual Studio solution explorer and only see the file which were touched in a pull request, like it was done in [PReview](https://github.com/laurentkempe/PReview).

We should also be able to associate the Pull request Filter button to keyboard shortcut.

Mockup

![Screenshot](https://farm1.staticflickr.com/735/22391690788_b9e60c9182_o.png)