rules: be verbose by default when creating diff

ruleset diff is more informative if we know at least when the
different sources have been updated.
rules: improve changelog template for ruleset
rules: display list of changelog

A list of changelog is now displayed and it is possible to display
any changelog.
rules: fix error in html
rules: add 'changed' field to 'sourceupdate'

Add field to store the number of change in a source update. This
will allow to only display significative entries.
rules: git version of rule is useless

It is only interesting for devel, we can hide it for now.