fix image endpoint, legendresource response

- replace ImageResourceController with ImagePublisher to serve
  ExternalGraphics from the style directory and gsr images
- fix inline image response in legendresource and add url, width,
  and height output
- antialias legend images
- remove superfluous 'params' from template routes and minor fixes
  related to format handling

This needs to get on 2.5.x as well for ROGUE