Bleach is deprecated

[seansica]

Per Mozilla, as of Jan 23, Bleach is deprecated: mozilla/bleach#698 (comment)

They will continue to provide security updates and bug fixes for approximately one year.

We need to replace Bleach.

ammonia looks like a promising solution but there may be others.

This is a good opportunity to refactor a bit. The process of sanitizing the HTML and generating the seed file (index.json) for the search index should be decoupled. There ought to be a separation of concerns between the generation of the website content and the generation of the search index.

Order of events:

1. Build website (Pelican/update-attack.py)
2. Generate seed file for search index (e.g., ammonia)
3. Generate search index (attack-search --> npm/webpack)