Auto-generate app manifests and optionally create Slack app through API

[DonDebonair]

By introspecting the plugins that are configured, it is possible to auto-generate a viable app manifest. This app manifest should include:

• The right scopes
• The right events to listen to
• Any Slack commands that need to be registered
• ...?

As an extra, we could even support creating the Slack app automatically using the manifest apis. This requires App configuration tokens