Use GTK3's GApplication/GtkApplication #178 (#181)

* Use GTK3's GApplication/GtkApplication #178
* fix: remove icons in menu
* doc: update CHANGELOG.md
* chore(i18n): update po/diffuse.pot

Co-authored-by: Yurii Zolotko <[email protected]>
Co-authored-by: Romain Failliot <[email protected]>

Author: 3 people

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Translation: updated Swedish translation (@eson57)
 - Dialog: prompt only once if several files needs to be reloaded (@yuriiz)
+- Use GTK3's Gtk.Application/Gtk.ApplicationWindow (@yuriiz)
 
 ### Fixed