Read CS versions from .json files, instead of hmlinter.yml

During discussion on the testing guild call today, we raised that several problems had arisen where linter bot and local linting got out of sync on various projects.

I'd like to propose that if an hmlinter.yml is not present, this bot could check composer.json and package.json if they exist in the project root and infer the correct coding standards versions from those files. We could even read these files even _if_ the yml file is present, so the bot could raise a warning that those versions had drifted out of sync.

@tomjn alternatively suggested that the linter bot could include in its PR comment a post which would list the versions of the dependencies which were used in the bot, and (in a details tag) a snippet for how to run the commands locally.

Either way, we should make it more obvious what version of things is in play, and make it easier for us and Altis clients to