Add language dependent tests

This is a first attempt for adding language dependent tests.

Setup: Multiple Devices with different language and region settings.

We wan't to test views on different devices with different language.
So you could do 
```objective-c
FBSnapshotVerifyViewWithLanguageCode(view, @"de_de", nil);
FBSnapshotVerifyViewWithLanguageCode(view, @"it_it", nil);
```

If you run the test on an device with the region setting `"de_de"` the first `FBSnapshotVerifyViewWithLanguageCode` runs against the saved image for `"de_de"`.

If you run the test on an device with the region setting `"it_it"` the first `FBSnapshotVerifyViewWithLanguageCode` is ignored, because it's the wrong locale. The second `FBSnapshotVerifyViewWithLanguageCode` runs against the saved image for `"it_it"`.

You could also run language independent test with the normal `FBSnapshotVerifyView` command.

The code isn't complete, but i like to start a discussion how to implement it.

What do you think?