fix(notifications): Better threading + resolve html entities decoding issue

* [x] Make Travis happy
* [ ] LGTM from 3 Elgg owners (@Srokap, @ewinslow, THREE)

Fixes #6894
That perhaps deserves a ticket. This change unifies our conversions among codebase, if we'd change it, perhaps we'd want to do it for all html entity operations in the same way.