breakup SSLSrvConfigRec in preparation for proxy support:

+ modssl_pk_server_t - certs/keys for the server
+ modssl_pk_proxy_t  - certs/keys for the proxy
+ modssl_auth_ctx_t  - stuff related to authentication that can also
                       be per-dir, used by both server and proxy
+ modssl_ctx_t       - context that can be used by both server and proxy
+ SSLSrvConfigRec    - now contains original stuff specific to the
                       server config and modssl_ctx_t *server, *proxy


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94267 13f79535-47bb-0310-9956-ffa450edef68