services: Split out layout management from EekboardContextService

Layout management was pointlessly bound with the EekboardContextService with inheritance. Splitting it out will make it easier to further break apart layout state management, settings, and input method in the future.

src/dbus.c

@@ -110,7 +110,7 @@ dbus_handler_new (GDBusConnection *connection,
 }
 
 void
-dbus_handler_set_context(DBusHandler *service,
+dbus_handler_set_ui_context(DBusHandler *service,
                              ServerContextService *context)
 {
     g_return_if_fail (!service->context);