#378 CIF data-based synthesis variable orders in separate classes

This is another step in #378 (closed):

• It mainly separates the variable orders, e.g., model/random/custom order, from the CIF to synthesis converter into separate classes, that allows them to be used multiple times. They are however not yet used multiple times. That will come later in #378 (closed).
• Moved and renamed some things, to make it all fit better. Reviewing separate commits is probably easier.
• Currently, a VarOrderHelper is created twice, once for the VarOrder and once for VarOrderer. This is temporary. It keeps the changes smaller for this merge request. It will be changed again in a later step. (Making progress while keeping everything backwards compatible after each step is tricky.)
• Another small change in CIF to synthesis converter: two variables named variables and curOrder had the same value, so one of them was removed.

Addresses #378 (closed)