Show plugin release date in plugin manager (#4535)

* Show plugin release date in plugin manager

* Add at-since

Co-Authored-By: Oleg Nenashev <o.v.nenashev@gmail.com>

* Make sorting work property

- Sort independently of sortable.js date parsing magic
- Hide categories when sorting by release date

* Show friendlier labels for the age of plugin releases

Co-authored-by: Oleg Nenashev <o.v.nenashev@gmail.com>