munin: add missing dependencies

* Add needed dependencies:
  coreutils, python, ruby, java and several Perl modules (Time::HiRes
  1.9.724 is no longer available, bump to 1.9725)
* Use sha256 instead of md5 (more secure)
* Wrap munin perl scripts so they find their dependencies at runtime
* Rework meta description attributes.

FIXME/TODO: munin is still not usable; it tries to write log files and
web graphs to its installation path.