Integration with Alloy

We originally attempted to strip Alloy out completely, but that didn't work, so the new approach is to bring Alloy and Kodkod together.

- Some new files were added to the multiobjective package
- Kodkod options was updated for multiobjective options
- Stubbed out the overflow functionality

Alloy expects Kodkod to have "int overflow" support. That way, the constraint `x < y + z` can be true even if `y + z` overflows. Unfortunately, the changes to Kodkod were too invasive to pull in, so I just stubbed it out.

The corresponding changes to Alloy are committed at 1c66dea52380bffcd58966ae8a750590a704c95a.