chore(views): improve ErrorPage css_class conversion

Examples:
- PageNotFound => page_not_found
- PageNotAllowed => page_not_allowed
- RecordNotFound => record_not_found
- ErrorPage => error_page
- HTMLError => html_error
- MyXMLParser => my_xml_parser

Author: blocknotes

lib/tiny_admin/views/pages/error_page.rb

@@ -16,8 +16,8 @@ def view_template
 
         def css_class
           self.class.name.split("::").last
-              .gsub(/([A-Z])/, '_\1')
-              .sub(/^_/, "")
+              .gsub(/([A-Z]+)([A-Z][a-z])/, '\1_\2')
+              .gsub(/([a-z\d])([A-Z])/, '\1_\2')
               .downcase
         end
       end