Improve/automatic width and height for subtitles

I guess you added this class to be able to test the private method.

On top of `HYPTextFormFieldCellTests.m` we could do

```
#import "HYPTextFormFieldCell.h"

@interface HYPTextFormFieldCell (Tests)

- (CGRect)labelFrameUsingString:(NSString *)string;

@end
```

Do have this behavior too