Change --auto-import to enum instead of having --auto-import-chapters, etc.

[sandreas]

An enum[] parameter with Chapters, Cover and other formats would be more flexible than having bool parameters for each purpose.

Maybe it would be even better to have an IMetadataImporter interface like this:

public interface IMetadataImporter {
     public string Identifier = "chapters";
     public Task<Status> ImportAsync(string path);
}

[sandreas]

Fixed in latest code.