Mutation tests UI

I've developed UI for mutation test infrastructure in order to simplify the process of running mutation tests.
Special menu items in DynamoView were created:
- Select tests - an ability to select tests to be run. List items are binded to CompositeCollection in MutatorDriver, where we dynamically build this collection from the available mutation tests marked with MutationTest attribute.
- Run here - run selected tests on the current document (RunMutationTests)
- Run on selected folder - an ability to run selected tests on saved files from the selected folder (RunOnSelectedFolder() function from MutatorDriver class).

 

Invert this condition for an early return (and make indentation of the code below better):

```cs
if (dialog.ShowDialog() != System.Windows.Forms.DialogResult.OK)
    return;
```