MEDIUM: tcpcheck: Refactor how tcp-check rulesets are stored

MEDIUM: tcpcheck: Refactor how tcp-check rulesets are stored

The tcpcheck_rules structure is replaced by the tcpcheck structure. The main
difference is that the ruleset is now referenced in the tcpcheck structure,
instead of the rules list. The flags about the ruleset type are moved into
the ruleset structure and flags to track unused rules remains on the
tcpcheck structure. So it should be easier to track unused rulesets. But it
should be possible to configure a set of tcpcheck rules outside of the proxy
scope.

The main idea of these changes is to prepare the parsing of a new
healthcheck section. So this patch is quite huge, but it is mainly about
renaming some fields.