Add support for WACZ creation.

[ikreymer]

This can be a command-line flag, say --generateWACZ similar to the --generateCDX option, which will generate a WACZ file after the crawl is done. This will also require keeping track of the pages crawled in a list that can be passed into py-wacz

This would involve:

• Adding a --generateWACZ command line option.
• Generate a pages/pages.jsonl file in the collection directory. Will need to make the pages dir also.
• Run py-wacz to create the WACZ at the end of the crawl. For now, can just regenerate the CDX during wacz creation. In the future, can use the existing index in redis to speed up the process.