Remove `hash_to_bytes` usage in the revision-content layer
It was only used for debug messaged and it's now replaced by bytes' `hex` method.
Add history graph structure to be used in the origin-revision layer algorithm
Also all uses of `hash_to_bytes` were removed from the graph module in favour
of bytes' `hex` method.
Refactor origin-revision layer algorithm to use the new history graph structure
Depends on D5880