create an interactive model for the systems chapter

[paulremo]

Make an interactive model for models 1,2, and 3 described here.

[paulremo]

There exists now a draft of this interactive model here.

There is one issue with the model: the way Models 2 and 3 are described here, the failure rate is infinity at the transition point where t=tau, if beta < 1. Two possible fixes:

• Allow only beta > 1 (currently implemented)
• Change the model definition to assume time-invariant lambdas for t <= tau instead of t < tau

[paulremo]

@csxADS: similarly to #65, please review the interactive system model and try to break it. Report any issues you encounter here:

• [x] Wear-out

[csxADS]

Same as #65

[paulremo]

Addressed in https://github.com/paulremo/NRPMInteractivity/issues/5