prefs: Add can-swipe-back compat with latest libadwaita

Recent libadwaita has renamed "can-swipe-back" into "can-navigate-back".
Set both in JS code instead of UI file in order to support all libadwaita versions.

Fixes #185

src/prefs.js

@@ -553,6 +553,11 @@ class ClapperPrefsWindow extends Adw.PreferencesWindow
             transient_for: window,
         });
 
+        /* FIXME: old libadwaita compat, should be
+         * normally in prefs UI file */
+        this.can_swipe_back = true;
+        this.can_navigate_back = true;
+
         this.show();
     }
 });

ui/preferences-window.ui

@@ -5,7 +5,6 @@
     <property name="resizable">True</property>
     <property name="search-enabled">True</property>
     <property name="destroy-with-parent">True</property>
-    <property name="can-swipe-back">True</property>
     <property name="modal">True</property>
     <child>
       <object class="AdwPreferencesPage">