dmails: replace hard deletions with soft deletions.

Turn deletions into soft deletions (set the is_deleted flag) instead of
hard deletions (remove from database). The is_deleted flag actually
already existed, but it was never used before.

app/models/application_record.rb

@@ -7,8 +7,10 @@ class ApplicationRecord < ActiveRecord::Base
         extending(PaginationExtension).paginate(*options)
       end
 
-      def paginated_search(params, count_pages: params[:search].present?)
+      def paginated_search(params, defaults: {}, count_pages: params[:search].present?)
         search_params = params.fetch(:search, {}).permit!
+        search_params = defaults.merge(search_params).with_indifferent_access
+
         search(search_params).paginate(params[:page], limit: params[:limit], search_count: count_pages)
       end
     end
@@ -93,7 +95,7 @@ class ApplicationRecord < ActiveRecord::Base
       end
 
       def search_boolean_attribute(attribute, params)
-        return all unless params[attribute]
+        return all unless params.key?(attribute)
 
         value = params[attribute].to_s
         if value.truthy?

app/models/dmail.rb

@@ -136,8 +136,6 @@ class Dmail < ApplicationRecord
       q = q.text_attribute_matches(:title, params[:title_matches])
       q = q.text_attribute_matches(:body, params[:message_matches], index_column: :message_index)
 
-      params[:is_spam] = false unless params[:is_spam].present?
-
       q = q.read if params[:read].to_s.truthy?
       q = q.unread if params[:read].to_s.falsy?