SOGo v2.3.23

Enhancements

• [web] added Simplified Chinese (zh_CN) translation - thanks to Thomas Kuiper
• [web] updated CKEditor to version 4.7.3

Bug fixes

• [core] yearly repeating events are not shown in web calendar (#4237)
• [core] correctly handle "Last day of the month" recurrence rule
• [core] fixed yearly recurrence calculator with until date
• [core] generalized HTML sanitization to avoid encoding issues when replying/forwarding mails
• [eas] avoid sync requests for shared folders every second (#4275)