the yaml module set had wordpress and drupal but not joomla, while the legacy
internal/scan/cms.go detects all three. the new module fills that gap so
--all-modules and -mt cms cover joomla too.
matches the generator meta (version-independent, joomla 1.5 through 5) plus
structural markers /media/system/js/core.js, /media/jui/ and
joomla-script-options, on the root and /administrator/. verified against live
and archived joomla sites, with no false positives on pages that only mention
joomla. version comes from a versioned generator or a leaked
X-Content-Encoded-By header.
additive: cms.go is untouched, the -cms scan is unchanged. whether converted
scanners should also run in the default flow is the open question on #52.
refs #52
