High: PE: Use hashtables instead of linked lists for performance sensitive datastructures

We spend a lot of time looking up known_on and allowed_nodes by ID, use a hashtable instead
Also, we spend a lot of time creating internal constraints,

• defer deletion ordering constraints until needed (rarely)
• remove unnecessary ordering constraints and logic

Mercurial revision: dc84927a4bb53be08f9c933623446a94057e9072