#689 Fix CIF explorer crashing on models with minimum integer value

• Best to review per commit.
• Code changes:
  • Fixes JavaDoc of CifValueUtil.makeInt.
  • Adds CifValueUtils.makeReal, similar to CifValueUtils.makeInt.
  • Fixes CifEvalUtils.valueToExpr for negative integer values.
  • Fixes CifValueUtils.getDefaultValue for integer types that only support negative values.
• End user changes:
  • Fixes 'add default init value' CIF to CIF transformation for discrete variables with an integer type that only supports negative integer values.
  • Fixes 'simplify values' CIF to CIF transformation to produce correct results for integer expressions that are simplified to the minimum integer value.
  • Fixes CIF explorer crash for models with expressions that evaluate to the minimum integer value.
  • Fixes CIF explorer crash for variables with integer types that only support the minimum integer value.
  • Fixes CIF pretty printer for integer types that only support the minimum integer value.

Closes #689 (closed)