Make extensions installable/updatable with Mechanic

[Mechanic](https://github.com/jackjennings/Mechanic) is an extension that allows RoboFont users to download and install extensions and keep them in sync with the version hosted on GitHub.

I've added the `repository` and `extensionPath` keys to your `info.plist`, in order to make the extensions in fbOpenTools installable and updatable through Mechanic. You can check out the [Developer section](https://github.com/jackjennings/Mechanic#mechanic-for-developers) to see how this works. Each time the version is updated in the `info.plist` file of one of your extensions, Mechanic will recognize the update and prompt your users to update to the most recent version.

If you would accept this pull request, I'll add the records to Mechanic's project registry so that these extensions can be installed through Mechanic's interface.