Fix: shortcut for provers which are unknown

Johannes, Yannick: yes this is what you think (good news)
but this is not yet completed (bad news)

But:
 - problem with BuiltIn, Bool, Tuple, Unit and theory
 - work only with "why" and "whyml" files format

warning for possibly useless quantifiers (unless a leading underscore is used)

Locations and labels were leaking into constant definitions, thus
preventing TPTP provers to unify them when equal. Example:
const_shdqproofssldtdtsltest_harnessdtmlwdq_17_23_24sh_3 <> const_3.

Indeed their inlining causes an exponential growth of the formulas for all
the provers that are relying on the "eliminate_if" transformation.

(in case of a prover upgrade)