Configure blacklisted VAPIs

Blacklisted VAPIs aren't scanned when Valencia first parses symbols,
meaning specific VAPI files can be skipped outright.  This is useful
when multiple VAPIs hold the same or similar symbols (such as gtk+-2.0
and gtk+-3.0, or gee-0.8 and gee-1.0) but a project is only using one
of them.