Add pre-moderation option

[DennieMello]

Thanks for this plugin! It would be great to add a pre-moderation mode for comments. Add the "moderation" property to each comment, similar to "blocked", and add a button to the admin panel, similar to "Hide comment". And also when changing or creating a comment, set the "moderation" status to true.

[cyp3rius]

@DennieMello can you describe in more details expected flow? Sounds interesting :)