Provide better documentation and UI for sources

[helrond]

Is your feature request related to a problem? Please describe.

For an added layer of security, it is possible for services to whitelist sources that they will respond to. This feature is not well documented, and there is no UI available for creating sources.

Describe the solution you'd like

Update documentation to describe this feature, and provide a UI for creating and updating sources.

Describe alternatives you've considered

There aren't really any alternatives here; we need to do this.