Also move User_Plugins#installPlugin to FijiTools

Same reason as User_Plugins#getMenuItem.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Moved another ImageJ 1.x patch to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Move the ImageJ 1.x windows' icon logic to ij-legacy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Remove the OtherInstance logic from fiji-compat

It made it into ImageJ 1.46f after years, so after 1.399 years it is
time that we removed our work-around.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
fiji-compat: -batch-no-exit handling moved to ij-legacy

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