IM3Reader for Perkin-Elmer Nuance

This is a basic reader for the Perkin-Elmer Nuance .im3 format. I don't have access to the file format spec, but I have a fair degree of confidence that the reader works. There isn't much in terms of metadata extraction.
Adding a call to ```FormatTools.checkPlaneParameters(this, no, buf.length, x, y, w, h)``` here is recommended, as that will handle all null and bounds checking on the given parameters.