- Removes arith_constants.h

- Removes arith_constants.h
- Adds ArithStaticLearner.  Consolidates and cleans up the code for static learning in arithmetic.  Static learning is now associated with a small amount of state between calls. This is used to track the data for the miplib trick.  The goal is to make this inference work without relying on the fact that all of the miplib problem is asserted under the same AND node.
- This commit contains miscellaneous other arithmetic cleanup.