Keyboard shortcuts for jumping around

Old:
- `<Esc>`: jump to parent
- `<Enter>`: jump to top-left child

Problem: `<Esc>` needs to be reserved for close pop-up menus, e.g., right-click menus.

Proposed:

- `<shift>-<up>`: jump to parent
- `<shift>-<down>`: jump to top-left child
- `<shift>-<left>`: follow indegree edge
- `<shift>-<right>`: follow outdegree edge