Make the default legacy editor implementation a low priority

Fiji wants to override it, so let's not make it a 50/50 game which one is taken by virtue of having exactly the same priority.

This *might* fix the problems reported with the legacy editor not supporting the ImageJ Macro language by Aryeh Weiss and Laurent Holtzer.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'master' of https://github.com/imagej/imagej