File import blacklist

[Zweibach]

I am primarily concerned about files imported through the API but I guess it could be useful for normal file imports too, with sidecar .txt files with tags, regex extraced tags from filenames, and the like.

While it would be preferable to have separate lists for the different contexts I'd be perfectly happy with a single one that applies to all non-downloader system contexts to start with.

As an example here I'll describe a situation: Somebody downloads a bunch of images using pixiv-util or gallery-dl to get all those ugioras and such. Together with that tags are downloaded and stored in a .txt file.
Then a script is used to import that file to Hydrus using the API, the tags are extracted from the .txt and formatted in a way acceptable to Hydrus.
Hydrus API gets the file (or just hash if you want to reduce network usage in case the transaction takes place between different computers) and tags.
Hydrus then checks the tags, sees a blacklisted tag and responds with "I do not have this file, and based on the tags I do not want it either". Or in more codey language something like Error 420.