Simpn

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- [Change] changed the semantics of queue tokens: now they are always available instead of at the time of the last token in the queue.

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- [Bugfix] if a layout contains a node not in the model anymore, it does not generate an exception.

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- [Feature] added queueing network prototypes.

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- [Feature] improved visualization of prototypes.

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- [Bugfix] store-checkpoint did not work correctly for SimVarTime.