feat(ui): style app menus and extract glossary dialog

- Add AppMenu and AppMenuItem so menu labels, mnemonics and shortcuts render consistently under org.kde.union
- Move the translation glossary into GlossaryDialog with add, remove and clear-all actions
- Regroup the translation preset and instructions settings layout

src/CMakeLists.txt

@@ -62,11 +62,14 @@ ecm_add_qml_module(qtpotato
 
 ecm_target_qml_sources(qtpotato SOURCES
     qml/Actions.qml
+    qml/AppMenu.qml
+    qml/AppMenuItem.qml
     qml/AudioMenu.qml
     qml/AudioTracksMenu.qml
     qml/FileMenu.qml
     qml/Footer.qml
     qml/GeneralSettings.qml
+    qml/GlossaryDialog.qml
     qml/HamburgerMenu.qml
     qml/Header.qml
     qml/HelpMenu.qml