IO: Added IO configuration parser
IO: Moved top level config to ezpublish

Added

ezpublish:
    system:
        default:
            io:
                metadata_handler: default
                binarydata_handler: default
IO: Made naming of ezimage io service consistent
IO: services declaration fix & cleanup

- Fixed usage of siteaccess config in services
- unified naming of handlers based on default config (default handlers are named 'default')
IO: Added default io_root_dir to default settings
IO: added handler factory
IO: Configuration parsing + compiler pass