x11-toolkits/ocaml-lablgtk2: the port had been hopefully improved (+)

• Amend USE_GNOME and convert to static pkg-plist as suggested by the stage Q/A; particularly, the latter should help track changes easier

• Add PORTSCOUT to limit the scope to versions we're interested: before it was picking up bogusly named `lablgtk2188' tag which corresponds to the older version 2.18.8; new tags are named sanely and consistently

• Push option definition and description block lower within the Makefile where it normally belongs

• Synchronize port description with upstream and remove references to ${PREFIX} and ${PORTNAME} from it as they are not expanded and this is not the right place to point users to the installed documentation in the first place; actualize WWW line while I'm here