Switch to using JS WACZ

[ikreymer]

Replaces dependencies on py-wacz with importing js-wacz natively.
Writes pages to either pages.jsonl (if seed) or extraPages.jsonl (if non-seed)
Uses streams for writing pages
Replaces --generateCDX with just moving tmp-cdx -> indexes
Removes any dependencies on python

Fixes #484

Pending more testing and js-wacz release, using @tw4l branch for now!

[tw4l]

Also noticing that js-wacz is logging strings to stdout, which breaks our logging format. Might want to see what we can do about that. I suppose if we call it as a subprocess via the cli we could capture the stdout and write it into the details of a crawler log line...

[tw4l]

TODO:

• Add WACZ validation (not yet supported in js-wacz)
• Make CDXJ handling more memory-efficient in js-wacz (currently keeps all pages in memory, may OOM with large crawls)
• Possibly move CDXJ line handling in js-wacz from bin/cli.js into WACZ class