GUI for configuring payment pointer

[michielbdejong]

In order to make https://github.com/solid/node-solid-server/issues/1513 more usable (i.e. so that the pod owner does not need to hand-edit json) it would be good if https://github.com/solid/solid-panes/blob/master/src/dashboard/basicPreferences.ts had a GUI widget for configuring the pod owner's payment pointer.