REORG: http: move the code to different files

REORG: http: move the code to different files

The current proto_http.c file is huge and contains different processing
domains making it very difficult to work on an alternative representation.
This commit moves some parts to other files :

  - ACL registration code => http_acl.c
    This code only creates some ACL mappings and doesn't know anything
    about HTTP nor about the representation. This code could even have
    moved to acl.c but it was not worth polluting it again.

  - HTTP sample conversion => http_conv.c
    This code doesn't depend on the internal representation but definitely
    manipulates some HTTP elements, such as dates. It also has access to
    captures.

  - HTTP sample fetching => http_fetch.c
    This code does depend entirely on the internal representation but is
    totally independent on the analysers. Placing it into a different
    file will ease the transition to the new representation and the
    creation of a wrapper if required. An include file was created due
    to CHECK_HTTP_MESSAGE_FIRST() being used at various places.

  - HTTP action registration => http_act.c
    This code doesn't directly interact with the messages nor the
    transaction but it does so via some exported http functions like
    http_replace_req_line() or http_set_status() so it will be easier
    to change only this after the conversion.

  - a few very generic parts were found and moved to http.{c,h} as
    relevant.

It is worth noting that the functions moved to these new files are not
referenced anywhere outside of the files and are only called as registered
callbacks, so these files do not even require associated include files.