Move first version to standalone directory

examples/acasxu.why

standalone/config.ml

standalone/config.mli

standalone/dune

standalone/engine.ml

standalone/engine.mli

standalone/main.ml

standalone/marabou.ml

standalone/marabou.mli

standalone/model.ml

standalone/model.mli

standalone/property.ml

standalone/property.mli

standalone/property_lexer.mll

standalone/property_parser.mly

standalone/property_types.mli

standalone/pyrat.ml

standalone/pyrat.mli

standalone/solver.ml

standalone/solver.mli