Add portal support(not finished).

1. add portal processor to extract links from portal sites.
2. add logic to generate block xpath, almost same with normal generate
process, but use any class because we can validate later, and normalize
selected element with more logic.
3. add logic to generate xpath for headline news, but for now just work
as normal news. need to improve.
TODO:
1. update xpath generating of headline.
2. add process to let user select normal news, and generate xpath by
selection.
3. finish portal selecting process, consider multiple blocks.