Admin users can mutate data while in preview mode

Currently, we rely on the client to validate whether or not a user is in preview mode and we block them from submitting forms. However, this validation does not happen on the back-end.

For example, we didn't setup proper client side validation to prevent an admin user from submitting the logo delete form while they were in preview. This can have unintended consequences if the admin user wrongly believes they are safe from mutating data while in preview.