Merge branch 'auth-improvements' into 'develop'

Cookie auth rework / Auth subsystem refactoring and tweaks

Closes pleroma/secteam/pleroma#3

See merge request pleroma/pleroma!3112

CHANGELOG.md

@@ -25,6 +25,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - The site title is now injected as a `title` tag like preloads or metadata.
 - Password reset tokens now are not accepted after a certain age.
 - Mix tasks to help with displaying and removing ConfigDB entries. See `mix pleroma.config`
+- OAuth form improvements: users are remembered by their cookie, the CSS is overridable by the admin, and the style has been improved.
+- OAuth improvements and fixes: more secure session-based authentication (by token that could be revoked anytime), ability to revoke belonging OAuth token from any client etc. 
 
 <details>
   <summary>API Changes</summary>