POM: depend on the ImageJ public group repository

The advantage is that this transparently links to _all_ repositories on
maven.imagej.net, instead of _only_ the ImageJ releases themselves.
POM: add monte-cc and javaoctave deps
Fix jex.statics class imports
Fix references to miscellaneous.StringUtility
POM: use jar packaging for xadisk dep
POM: fix javax.mail dependency