Add support for quantifiers

[feliperodri]

We still need to address a few issues:

• Avoid code duplication;
• Ensure CBMC doesn't ignore the quantifier expressions due to side effects (we should probably use lambda expressions);
• Only enable quantifiers with unstable flag;
• Add more regression tests to test UI;
• Extend RFC 0010-quantifiers to include explanation on how Kani is building the quantifier expressions;

Resolves #2546 and #836.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[gmorenz]

I've rebased this branch on master, with a few necessary updates, here: https://github.com/gmorenz/kani/tree/quantifiers