Fix IJ1Helper#updateRecentMenu in headless mode

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Touch up recent file handling

Let's not let ImageJ 1.x do its thing; who knows what it will do in
future versions. Let's just add the listener so that the new entries
work.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'recent-images'

This branch works on the handling of recent image items, addressing an
issue raised by Paul van Schayck.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>