sj-hierarchy.pl: simplify some tests
sj-hierarchy.pl: stop caching parent projects

This cache used to be necessary when the parent was computed by calling
maven-helper.sh, but now that we extract it directly from XML which is
itself cached in memory, there is no need for an extra caching layer.
sj-hierarchy.pl: split script into three functions

Each function is now accessible with a separate command line flag.
sj-hierarchy.pl: add SCM extraction routine
sj-hierarchy.pl: fix inaccuracy in comment
sj-blacklist.txt: add more obsolete artifacts
sj-hierarchy.pl: add option to dump SCM URLs