pm_reduce just reduces away proof mode terms using cbv; pm_prettify just prettifies user-visible connectors using cbn.
Most uses of pm_default are converted to default to keep the desired reduction behavior.

List literals reduce with a spurious `emp` at the end, which is not pretty.

With a pretty proof by Robbert

make pm_maybe_wand a BI connective; reduce BI connectives and option combinators in the proofmode with cbn

We already do the same for the goal, this avoids some scope
delimiters being displayed.

move test suite out of theories/ so it does not get installed; also check output of test suite so that we can test printing