Resurrect part of the updater fix as binary .plist disassembler

This script was extremely helpful when debugging the switch from
imagej-legacy's ImageJ2Options from a modal to a non-modal dialog
because on MacOSX, the preferences are stored in a binary
$HOME/Library/Preferences/net.imagej.legacy.plist file.

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