Fix resources build errors

I found the following build errors when trying to build solution:

```
App.xaml.cs(9,34): error CS0234: The type or namespace name 'Resources' does not exist in the namespace 'FluentAssertions.WP8.Specs'
LocalizedStrings.cs(1,34): error CS0234: The type or namespace name 'Resources' does not exist in the namespace 'FluentAssertions.WP8.Specs'
MainPage.xaml.cs(10,34): error CS0234: The type or namespace name 'Resources' does not exist in the namespace 'FluentAssertions.WP8.Specs'
LocalizedStrings.cs(10,24): error CS0246: The type or namespace name 'AppResources' could not be found
LocalizedStrings.cs(12,16): error CS0246: The type or namespace name 'AppResources' could not be found
```

I'm not sure where they are used or what for, but just fixed them up with ReSharper.

HTH