#458 CIF/BDD: Introduce and use CifBddDomain, replacing JavaBDD's BDDDomain.

• Best to review per commit.
• No end-user visible changes.
• Changes:
  • Added CifBddDomain, to replace JavaBDD's BDDDomain. CifBddDomain doesn't know anything of what its bits represent.
  • Domains are created via CifBddSpec, which stores the created domains. CifBddSpec gets getDomainCount, createDomain and createDomains.
  • BDD domain variable sets are now properly freed at the end of synthesis. This leads to an extra sample in continuous BDD metrics, as can be seen in a data-based synthesis test output change.
• Note that we still only use BDD domains to represent non-negative values. There are steps to follow still in #458 (closed).

Addresses #458 (closed)