Extended ImageReaderFactory to be able to use ImageIO ServiceRegistry to
load the third party image readers (the default dcm4che2 behavior).
Default loading mechanism is still ServiceLoader. Too use the ImageIO
ServiceRegistry option you must set the following java system property:
-Ddcm4che.useImageIOServiceRegistry=true
Merge pull request #9 from vmerkel/master

Extended ImageReaderFactory to be able to use ImageIO ServiceRegistry again