Tutorial for ECG computation

As we (now) also support pseudo-bidomain and phie recovery, it would be nice to also cover that in the examples.

There are related carpentry examples:

• https://carpentry.medunigraz.at/carputils/examples/tutorials/tutorials.02_EP_tissue.07_extracellular.run.html
• https://carpentry.medunigraz.at/carputils/examples/tutorials/tutorials.02_EP_tissue.07A_augmentation.run.html (Augmentation to be excluded)