Support accels for menu items

Add support for keyboard shortcuts for menu items. Additionally enable a common Ctrl+O for opening new file(s) and Ctrl+U for opening an URI.

Closes #45

src/menu.js

@@ -2,12 +2,18 @@ const { GObject, Gtk } = imports.gi;
 const Dialogs = imports.src.dialogs;
 
 var actions = {
-    openLocal: (window) => new Dialogs.FileChooser(window),
-    openUri: (window) => new Dialogs.UriDialog(window),
-    prefs: (window) => new Dialogs.PrefsDialog(window),
-    about: (window) => new Dialogs.AboutDialog(window),
+    openLocal: {
+        run: (window) => new Dialogs.FileChooser(window),
+        accels: ['<Ctrl>O'],
+    },
+    openUri: {
+        run: (window) => new Dialogs.UriDialog(window),
+        accels: ['<Ctrl>U'],
+    },
+    prefs: {
+        run: (window) => new Dialogs.PrefsDialog(window),
+    },
+    about: {
+        run: (window) => new Dialogs.AboutDialog(window),
+    },
 };
-
-var accels = [
-    ['app.quit', ['q']],
-];