POM: remove unused args4j dependency
Use SciJava standard package and artifact name

The Java package prefix should be net.imagej.omero since the ImageJ
project is centered at imagej.net.

The artifact should be imagej-omero since that is the convention for all
other SciJava project organizations: SCIFIO (io.scif), ImgLib2
(net.imglib2) and SciJava itself (org.scijava).