Tool: Build a Probot to automatically check npm maintainers

[RichardLitt]

This tool ought to:

• Be turned on for each OrbitDB repo
• Automatically check the package.json on a change
• Run npm info and parse out the maintainers output
• Check that this matches orbitdb.maintainers in the package.json
• If it doesn't, automatically PR the change to the repository

This will keep our orbitdb.maintainers field up to date without needing extra configuration from the authors.