Ignore pages with 0% unique text blocks

[laurentprudhon]

Example : https://www.60millions-mag.com/forum/banque-epargne-credit-f76/

1228 out of 1978 pages contain 0% unique text blocks.

• Don't write a file on disk if it contains 0 unique text block
• Don't include this file in the stats to compute a early stopping condition
• Don't crawl links on this page

[laurentprudhon]

Only implemented point 1