680 implement lct model

[lenaploetzke]

Changes and Information

Please briefly list the changes made, additional Information and what the Reviewer should look out for:

• added additional model based on the Linear Chain Trick.

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Closes #680

[mknaranja]

@dabele I would like to merge this for the functionality first (except for small adaptations that go in the right direction maybe) and then create a new issue to adapt/generalize the new model to our compartmental or flow model base classes. I think this needs then also adaptations of the ODE models. Maybe you could have a look and write down what your redesign suggestions are?

[lenaploetzke]

This PR is divided into several smaller issues to make it easier to review. Have a look at

• Implement simple LCT model #892 (main model)
• Add initialization method with real data for LCT model  #893
• Add initialization method from flows for LCT model #897
• Change test for valid transition distribution from ide model #898
• Add gamma distribution and other parameters to state_age_function #899
• Add function to change the tolerance in IDE model #918