Update examples

[ThibeauWouters]

To improve documentation and help new users get started easily with flowMC, we should update the examples directory. Here are some suggestions and ideas, but I am open to feedback:

• Update examples to work with new flowMC version
• Perhaps only use Python notebooks rather than both notebooks and Python scripts, as they are more suitable for adding documentation and explaining the structure of the code and how to use/adapt it
• Add other commonly used datasets for benchmarking flowMC, such as the Rosenbrock function