Rename LanguageViewLocationExpanderOption to LanguageViewLocationExpanderFormat

It's not just an option, it's specifying the format of the location.

Also, while there, need to fix a typo in the comment: [`exisits`](https://github.com/aspnet/Mvc/blob/dev/src/Microsoft.AspNet.Mvc.Razor/LanguageViewLocationExpanderOption.cs#L12)
