Mastodon API: Fix lists leaking private posts

Our previous list visibility resolver grabbed posts if either follower
collection of the user in a list who is followed is in `to` or if
follower collection of the user in a list was in `cc`. This not only
missed unlisted posts but also lead to leaking private posts when
`fix_explicit_addressing` mistakingly started putting follower collections
to `cc` (also fixed in this MR).

Reported by @kurisu@iscute.moe via a DM

CHANGELOG.md

@@ -118,6 +118,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## Removed
 - Configuration: `config :pleroma, :fe` in favor of the more flexible `config :pleroma, :frontend_configurations`
 
+## [0.9.99999] - 2019-05-31
+### Security
+- Mastodon API: Fix lists leaking private posts
+
 ## [0.9.9999] - 2019-04-05
 ### Security
 - Mastodon API: Fix content warnings skipping HTML sanitization