open audio: if a plugin is being viewed, all projects which contain that plugin should be listed somewhere on that page

[RustoMCSpit]

open-audio-stack/open-audio-stack-registry#23

Project - File which contains song data, in a format only for a specific DAW(s).

also this should be vice versa, if a project is being used all plugins in the registry should be listed whilst those that are not will just be their name and "not available".

moved here at dromer's request