Add ARGC_OPT enum to provide more context for upcoming sample parse errors
involving proxy "option" config directives.

For a long time we couldn't have arguments in expressions used in
tcp-request, tcp-response etc rules. But now due to the variables
it's possible, and their context in case of failure to resolve an
argument (e.g. backend name not found) is not properly reported
because there is no arg context values in ARGC_* to report them.

Let's add a number of missing ones for tcp-request {connection,
session,content}, tcp-response content, tcp-check, the config
parser (for "set-var" in the global section) and the CLI parser
(for "set-var" on the CLI).

Due to the addition of the OpenTracing filter it is necessary to define
ARGC_OT enum.  This value is used in the functions fmt_directive() and
smp_resolve_args().

The ARGT_PTR argument type may now be used to keep a reference to opaque data in
the argument array used by sample fetches and converters. It is a generic way to
point on data. I guess it could be used for some other arguments, like proxy,
server, map or stick-table.

There are list definitions everywhere in the code, let's drop the need
for including list-t.h to declare them. The rest of the list manipulation
is huge however and not needed everywhere so using the list walking macros
still requires to include list.h.

This patch fixes all the leftovers from the include cleanup campaign. There
were not that many (~400 entries in ~150 files) but it was definitely worth
doing it as it revealed a few duplicates.

The stktable_types[] array declaration was moved to the main file as
it had nothing to do in the types. A few declarations were reordered
in the types file so that defines were before the structs. Thread-t
was added since there are a few __decl_thread(). The loss of peers.h
revealed that cfgparse-listen needed it.

A few includes (sessions.h, stream.h, api-t.h) were added for arguments
that were first declared in function prototypes.

There is no C file for this one, the code was placed into sample.c which
thus has a dependency on this file which itself includes sample.h. Probably
that it would be wise to split that later.

Almost no change was needed; chunk.h was replaced with buf-t.h.
It dpeends on types/vars.h and types/protocol_buffers.h.