Merge branch 'develop' of https://git.iws.uni-stuttgart.de/inversemodeling/bayesvalidrox into develop

Two tests for the ExpDesign became unneded due to change in the input parameters of ExpDesigns.generate_ED()

A first draft of the contribution guidelines can now be found in `CONTRIBUTING.md`.
The website was rebuilt, but does not include the guidelines yet.

User guide startet for models, surrogate training, sequential training, postprocessing and BAyesian classes. The guide now contains simplified UMLs (for BayesInf not yet done).

Webpage includes quickstart, user guide, tutorial, example collection and api.
One new example was added for the user guide.

Build api pages with autosummary and modified templates to include class documentation.
Tutorial updated to BVR 1.0.0 (engine use).

Copied the first version of the sphinx documentation into the docs/source folder. It can be built in html format with '.\make html'.
This includes start of API documentation, summaries of the examples and a tutorial for the 'analytical function' example for BVR version 0.0.5.

Errors thrown by the tests were resolved where possible.
If they could not be resolved and issue was created for them.
For the sake of testing the pipeline, the unresolved tests were commented out.

Changed scipy, tqdm, statsmodels

An example 'principal_component_analysis' was added to specifically test this functionality. It uses the analytical model.
Fixed two if-calls in `pca_transformation` to match older code and the content of the function.