Transient heat transfer: further TODOs

[dlohmeier]

With PR #533 , a lot of changes and further development has been implemented on the transient heat transfer branch. Before we can release the transient heat transfer simulation, there a still quite a few improvements to be implemented and things to clarify:

• get rid of "dynamic_simulation" option and consolidate it within the transient simulation
• make the new dynamic components and the controllers a bit more generic if possible
• adapt the controllers further to make them fit better into the pandapower control scheme
• ensure that the new dynamic components can be used in stationary mode as well (you shouldn't have to use a new network model in order to switch between stationary and transient mode)
• improve the initialization of the model in transient mode --> just using the pit of the previous time step prevents updating settings between time steps (e.g. pressure or temperature at the ext_grid)
• convert the python scripts on transient simulation in the tests to real tests and jupyter notebook tutorials
• write tests for the new dynamic components
• check overall test coverage (76% after the PR is not sufficient)
• check which of the controllers are useful and which ones might be too specific for general usage (e.g. CollectorController and LogicController might be fused into one controller that just combines values from another controller with a certain logic)
• make changes to pandapower (esp. time series) to ensure that everything works --> here, the aspect of the "time_step" kwarg is especially important, as it is not passed over to the pipeflow call as kwarg, since it is already used in the time series implementation

[dlohmeier]

Please comment or extend the list, if you have any further ideas, @Theda-ISE @EPrade