Changes

===Interface for handling and selecting custom filters on selectors===

* [https://developer.gnome.org/hig/stable/ GNOME Human Interface Guidelines]

* [https://raw.githubusercontent.com/gnome-design-team/gnome-mockups/master/nautilus/nautilus-next/search-filters-wires.png Mockups] and [https://csorianognome.wordpress.com/2016/02/08/nautilus-3-20-and-looking-forward/ new features] since gtk+ 3.20.