Proposal for #13165

This introduces changelink to foreign key widgets in the admin. The link will adapt to the currently selected object with the power of JavaScript. If no object is selected, the link disappears.

### Caveats

The change link adapts when a different object is selected. JavaScript is replacing the /\d+/$ URL part with a different ID. This looks safe and is apparently the best there is for resolving admin links in JS.

### Open Questions

1. Should readonly_fields have a change link? Currently they don't.
2. Should raw_id_fields hava a change link (that adapts to the value)? Currently they don't, probably yes.
3. Should radio_fields hava a change link?  Currently they don't, probably yes.
4. How should multipleSelect fields be handled? Currently they are not, displaying links not that easy.
5. Should the change icon be placed before or after the add icon in the normal fk widget?
6. Change Icon needs some padding or other UI love.
7. The JS part is currently in actions.js, but has nothing to do with admin actions. Could not find better place, may need a new file. Suggestions welcome.
8. The text for the link in the inline admins is "edit separately" (from the original author). The usual copy in the admin is "change" instead of "edit". Suggestions welcome.