Add runtime dependency on imagej-legacy

For testing the script interpreter with the ImageJ 1.x macro language.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Curtis, please help me!

See also https://twitter.com/PavelTomancak/status/482603126781145088

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