Add contextual information to “The rate of a Markovian transition is zero or negative.” error.

The “The rate of a Markovian transition is zero or negative.” error currently gives the user no contextual information of where or why this is happening in their model. Having this makes it much easier for them to debug this error.

As an example, we can trigger this error in the bitoin-attack model from the case studies by giving it the parameters: -E "MALICIOUS = 20, CD = 6".