LemonSync should be able to call out to npm modules or other shell scripts

[robotpony]

A customer asked for a way to reload their browser after lemonsync completed each sync (a pretty typical use case).

Use cases

• trigger post-sync tasks like browser refresh
• trigger cleanup tasks
• trigger notification (system)

Via: https://app.intercom.io/a/apps/7236196445273cea007287c0c90a2f0d598567cc/inbox/inbox/all/conversations/16274401107