[New Content]: link to planning.domains editor to allow people to live code

[nergmada]

New Content Proposal: Planning.domains editor behaves like a fiddle. We can integrate demo domains from the reference guides to allow users to hop in and use the domains

Section: Reference & Guide PDDL

Justification: Because it's awesome

[haz]

You just mean links to sessions with pre-loaded PDDL? We do this for the PDDL book, and it works quite well.