Version 3.15.1
--------------

 * Modernize the GUI (Allan Day, Jente Hidskes, Felix Riemann)
 * Migrate to GAction (Jente Hidskes, Felix Riemann)

Bug fixes:

 #740426, Use a header bar (Allan Day, Jente Hidskes, Felix Riemann)
 #741050, Migrate to GAction (Jente Hidskes, Felix Riemann)
 #742369, doesn't use high quality icon in the overview (Andreas Nilsson)

New and updated translations:

- Daniel Martinez [an]
- Marek Černocký [cs]
- Dimitris Spingos (Δημήτρης Σπίγγος) [el]
- Daniel Mustieles [es]
- Iñaki Larrañaga Murgoitio [eu]
- Fran Dieguez [gl]
- Yosef Or Boczko [he]
- Balázs Úr [hu]
- Sveinn í Felli [is]
- Aurimas ÄŒernius [lt]
- Hannie Dumoleyn [nl]
- Rafael Ferreira [pt_BR]
- Stas Solovey [ru]
- Dušan Kazik [sk]
- Trần Ngọc Quân [vi]

New and updated manual translations

- Christian Kirbach [de]