- Move some methods into their own classes in order to make it easier
to reuse them outside of classes extending the base importer. For
compatibility reasons the old methods are still in the base importer
and delegate to the new objects. The following methods and hashes were
extracted:
- all the lookup maps for existing and imported data
- all the methods used for uploads and attachments
- No need to store failed users and groups. This information wasn't
used anyway.
- Print progress instead of category names when importing categories.
- Allow importers to override if bbcode_to_md should be used (until now
it always used ARGV)
- Allow importers to add additional site settings that automatically get
restored after the importer finishes.
- Show how many posts and messages are imported per minute. This should
help detecting when the import is slowing down and needs to be
restarted.
- Use max_image_width and max_image_height from settings instead of
hard-coded values for uploaded images.
