Allow to modify bookmark shortcuts in the shortcuts editor

It is possible to define keyboard shortcuts for quick access to bookmarks in accels.scm. E.g:

(gtk_accel_path "\<Actions\>/ThunarBookmarks/be6b46ea599d328913513e2dc6eba7d7" "\<Primary\>\<Alt\>1")

However, these shortcuts currently cannot be altered in the thunar shortcuts editor.

It would be nice to have the possibility to modify such shortcuts in the shortcuts editor, and to see the assigned shortcuts in the bookmark menu and in the shortcuts sidepane.