fixes wikimedia-gadgets#1974

- Did an all repo, case sensitive search and replace of Twinkle.fluff -> Twinkle.rollback
- Did an all repo search for "fluff" and changed remaining results to "rollback"

IMPORTANT: requires modifying https://test.wikipedia.org/wiki/MediaWiki:Gadgets-definition and https://en.wikipedia.org/wiki/MediaWiki:Gadgets-definition

IMPORTANT: may also require creating/renaming "Module: rollback" tag in the GitHub issue tracker, so that the PR labeler doesn't break

Because of the gadget definition file changes, should be careful with this one. May want to do a deploy to testwiki before deploying to enwiki.

Note to self: I haven't manually tested this yet. Manually test it before merging.