#530 Merge variable orders and orderers for CIF data-based synthesis variable ordering

• Builds upon the branch from !498 (merged), which hasn't been merged yet.
• I started with branch 530-merge-orders-and-orderers-for-cif-data-based-synthesis-variable-ordering, and then recreated the whole thing in branch 530-merge-orders-and-orderers-for-cif-data-based-synthesis-variable-ordering-2. This merge request is based on the latter. This merge request is reviewable per commit. I spent considerable effort to make sure changes are not reverted by subsequent commits.
• The changes in this branch are fully in line with the spirit of what is described in the issue description of #530 (closed). However, they are not exactly implemented as such.
• See the commit messages of the separate commits for the details.
• This merge request simplifies the design quite a bit, but also generalizes things to make it more expressive/powerful.

Closes #530 (closed)