Tracing tool: inherit basic actions from Navigator

This removes the navigation actions (zoom, pan) from the
Tracing tool and instead inherits them from Navigator.

It also removes a keycode ambiguity between '.' and 'DEL'. Moving
down in z now only works with the actual '.' key and not anymore with the one
on the numeric keypad. Before, in Navigator, one could also move down
in z with the 'DEL/.' key on the numeric keypad. However, this key is
used to delete the active node in the Tracing tool.