UMBridge examples cleaned and pylink 'single-valued' removed

Solved some issues from rebasing

OLS constraint directly to be set in the MetaModel source code. Small regression comparison as example for the constraint. No unit tests yet for the feature

Added a minimal test based on pylink classification. More work needed for higher-dim. model outputs here

In this scope the multiprocessing for running the models does not seem to work correctly anymore

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

Code updated for static training, tests not done yet

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)

Started testing MetaModel while also refactoring a bit more by moving code between ExpDesign and MetaModel

Added tests for Inputs and started on those for ExpDesign.
Regarding the second there are some open questions noted in issue #32