MEDIUM: http-rules: Register an action keyword for all http rules

MEDIUM: http-rules: Register an action keyword for all http rules

There are many specific http actions that don't use the action registration
mechanism (allow, deny, set-header...). Instead, the parsing of these actions is
inlined in the functions responsible to parse the http-request/http-response
rules. There is no reason to not register an action keyword for all these
actions. It it the purpose of this patch. The new functions responsible to parse
these http actions are defined in http_act.c