CodeHacker#replaceMethodCall(): allow replacing super()

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Let the LegacyExtensions know whether we're patching for headless mode

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure that a hidden ImageJ 1.x main window stays hidden

It seems that the showDialog() method of an AWT Dialog insists on showing
the owner window , at least on MacOSX, bypassing setVisible(). That's no
good if the main window is supposed to stay hidden.

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