Some simple fixes for various test, start on testing BayesInf, output directory as changeable parameter in BayesInf

Got started on these two tasks, restructuring still needs a lot of work here

New class 'Engine' responsible for both training sequentially and non-sequentially.
Currently training with old MetaModEngine and in MetaMod directly still possible, but will be deprecated and removed soon.
Also started splitting ExpDesign into InputSpace (for MetaMod, created dists and polynomials) and ExpDesign (for Engine, can also sample)