* [GRAPH_GENERIC,SC] About halfway cleaning this module up / moving parts to GRAPH_THEORY.
* [GRAPH_THEORY,NEW] New module, a reimplementation of all graph theory predicates in PLC.
* [LIST_EXT,SC] Moved sorting predicates to SORT_EXT.
* [PL_MODE,NEW] Added call_ground_as_semidet/1.
* [UGRAPH_EXT,SC] Cleanup / move to GRAPH_THEORY.