Added validations in 'instances_select_by_popular' method.
Better validations.
Added validations in 'instance_create' method.
Added validations in 'generators_select_by_new' method.
Added validations in 'generators_select_related_by_display_name' method.
Added validations in 'generator_select_by_url_name_or_generator_id' method.
Added validations in 'instances_select_by_new' method.
Added validations in 'instance_select' method.
Added validations in 'content_flag_create' method.