Avoid creation of proper SOM objects where possible

The strategy is here to rely on central points that cast to SAbstractObjects and create the SOM objects when necessary. Until then, objects can remain 'unboxed'.

[TODO-REPORT: describe this strategy]
[TODO: look into the arithmetic primitives that don't use ExactMath, and try to avoid Object as return type for situations involving int and BigInteger, try to use rewriting on exception]

Signed-off-by: Stefan Marr <git@stefan-marr.de>