Webhook support - create AtomicData by calling a webhook

[joepio]

Create instances of resources in one specific scope (parent) without needing an Agent / Commits / Token or whatsoever. Just send a POST request with a JSON body to that webhook and you're done!

When is this useful

• Linking to other services / integrating with other tools (through hubs like IFTTT). For example: create a person every time a form has been submitted on airtable.

How to build this: ClassExtender plugin

• We create a new WebHook class + ClassExtender (plugin)
• They have a certain target where they write the information
• They have a POST handler that parses the incoming JSON and creates a new resource in the hierarchy, at the target location.
• The rights of the Agent who created the WebHook are checked when creating a new resource through that webhook.

Not to be confused with

The other direction in which webhooks can work: as notifications when something in AtomicServer changes #77. This is also very valuable, but for a different usecase.