Expose tag blacklists for remote tag services through the API

[roachcord3]

I would like to be able to get the PTR's (or any remote tag service's) tag blacklists from the API. I feel like the "most natural" way to get this would be as part of the Services Object, perhaps only adding it if the user provides an optional parameter when making an API call to /get_service or /get_services.

My use case is that I would like to be able to programmatically rewrite pending tags that would be impacted by the blacklist so that they're unnamespaced (with optional disambiguators,) rather than expect parser developers to create tons of special cases to keep up with the moving target that is the PTR's blacklist, to say nothing of non-PTR remote tag services. E.g.:

• if substance:glue is pending, replace it with glue (default behavior of my program)
• if substance:slime is pending, replace it with slime (substance) (behavior of my program when user specifies that substance:* tags should be given disambiguators.)