MEDIUM: ssl/ckch: make the ckch_conf more generic

MEDIUM: ssl/ckch: make the ckch_conf more generic

The ckch_store_load_files() function makes specific processing for
PARSE_TYPE_STR as if it was a type only used for paths.

This patch changes a little bit the way it's done,
PARSE_TYPE_STR is only meant to strdup() a string and stores the
resulting pointer in the ckch_conf structure.

Any processing regarding the path is now done in the callback.

Since the callbacks were basically doing the same thing, they were
transformed into the DECLARE_CKCH_CONF_LOAD() macros which allows to
do some templating of these functions.

The resulting ckch_conf_load_* functions will do the same as before,
except they will also do the path processing instead of letting
ckch_store_load_files() do it, which means we don't need the "base"
member anymore in the struct ckch_conf_kws.