SMT2 refactored solver configuration

allow to dynamically choose the name of the solver executable and the arguments
added two options (solver_executable and solver_arguments) to select particular command line solver
fixed linking issues with duplicate named symbol support::execute
Boolector: avoid to depend on Btor* directly use result_type instead
Boolector: adapted result_type to the Boolector API 1.5.115
rewrote BtorExp* to BtorNode* in boolector_factorization
removed executable flag from Priority_Context.hpp
added an evaluator test case
updated bootstrap.sh to boolector-1.5.116
implemented reading from select expressions in SMT2 (fixes Array/read_value_t)
generalized constructor of metaSMT::type::TypedSymbol
renamed Array test case read_value_t to read_value_from_select
updated boolector version in bootstrap to 1.5.118
implemented Evaluator extension for read_value(.)
added UtreeEvaluator methods to analyse parsed SMT2 formulas
and transform them to metaSMT
added recognition of constants true, false
added recognition of more bv operators
added "ToString" to Methodnames generating strings
as preparation for generating result_types instead of strings
added Method to create Boolector::assumption/assertion instead of std::string
(does not calc result_type yet)
added method to translate SMT2 to result_types, works only for constants yet