Bump 3.17.4 release

The To Do development team proudly announces the
availability of GNOME To Do 3.17.4, the latest
public release under GNOME umbrella!

News for this version:

        * Fix wrong name throughout the application
        * Better represent visually task priorities by changing the row's color
        * Make edit panel resizable
        * Add "Today" and "Scheduled" custom lists
        * Improve notification system
        * Initial support for search over list names

        * Greek (Dimitris Spingos)
        * Hebrew (Yosef Or Boczko)
        * Polish (Piotr Drag)
        * Spanish (Daniel Mustieles)
        * Slovak (Dušan Kazik)
        * Slovenian (Matej Urbančič)