The STCN script now runs well into the various scrpaing stages of Picarta Web pages.

* [PICARTA_QUERY,EXT] Use the STCN generics to determine whether a link on a Picarta Web page refers to a PPN-denoted resource or not.
* [STCN_GENERIC,SC] Simplified all PPN-related predicates. Changes throughout the STCN and PICRATA modules.
* [STCN_SCRIPT,EXT] Distinguished several (sub)stages in the part of the script that deals with scraping Picarta.