Merged.

Hashing by ID is exactly what we want. No need to review, please merge.

Hashing by id is fine, isn't it? I fixed the bug using the action instead of its
name as key in the heavy action dict. On the benchmark instances, this has no
effect on the translator output (run time is fine as well).

Malte, would you like to review the change or should I simply merge it?

It looks like pddl.Action doesn't implement a __hash__ method, so if we just
hash the action itself, we'll get hashing by ID.

BalanceChecker.get_heavy_action relies on the assumption that action names are
unique. This is not necessarily the case after normalization. We should use the
id instead.