also show function definitions for higher-order free variables in Z3 models

always add pair rules and function update rules automatically (Boogie provides pairs and function update as built-in concepts and does not generate background axioms for them)

re-implemented eta-expansion, lambda-lifting, and explicit application on terms (exploiting the control over the term structure); abolished SMT interface concept in favor of solver classes (now also the translation configuration is stored in the context); proof reconstruction is now expected to return a theorem stating False (and hence needs to discharge all hypothetical definitions); built-in functions carry additionally their arity and their most general type; slightly generalized the definition of fun_app

re-ordered SMT normalization code (eta-normalization, lambda abstractions and partial functions will be dealt with on the term level); added simple trigger inference mechanism; added syntactic checks for triggers and quantifier weights; factored out the normalization of special quantifiers (used to be in the eta-normalization part); normalization now unfolds abs/min/max (not SMT-LIB-specific); rules for pairs and function update are not anymore added automatically to the problem; more aggressive rewriting of natural number operations into integer operations (minimizes the number of remaining nat-int coercions); normalizations are now managed in a class-based manner (similar to built-in symbols)