Remove problematic language

We should remove historically problematic language from Jetpack:

- [x] Grandfathering (done in #16050).
- [ ] Blacklist & whitelist (#16109, #16166, #16192)
- [x] Use of core WordPress functions now deprecated, such as `wp_blacklist_check` in `modules/contact-form/grunion-contact-form.php` (https://core.trac.wordpress.org/changeset/48121) -- https://make.wordpress.org/core/2020/07/23/codebase-language-improvements-in-5-5/ #16568 #16569
- [ ] Master & slave, etc
- [x] Switch from the use of the `master` branch as the default branch to `trunk`. Related discussion: p4TIVU-9rA-p2
- [ ] "Sharedaddy" as the underlying technical name to the Sharing module.
- [ ] "Masterbar" as the underlying technical name to the WordPress.com toolbar module.

"Blacklist" and "Whitelist" are used in a lot of places within Jetpack, so we should open separate PRs to address in chunks.