Add a regression test verifying that open() in batch mode works

This adds a simplified version of Paul van Schayck's macro, making
use of imagej-legacy's own icon resources to verify that images can
be loaded properly in headless mode, and that the particle analyzer
manages to find the particles, too.

The original mail thread describing the problem can be found here:

	http://thread.gmane.org/gmane.comp.java.imagej/33046

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