Add option to disable "Play Online" when online interpreters are buggy

[dfabulich]

It would be nice to add the option to disable "Play Online" for a particular external link.

This could make sense for games like The Purple Pearl where there's no one primary download, or for games that don't work in Parchment, e.g. curiousdannii/parchment#161

Currently it's kinda possible to do it either by putting another "Play Online" link earlier in the list of links (since the big blue "Play Online" button just picks the first online-playable link off the list) or if you set invalid filetype data for the file, tricking IFDB into thinking that the file is unplayable.