Incorporate `callback` function to handle exceptions in objective functions

[brosaplanella]

At the moment, if an evaluation of the objective function crashes, the whole optimiser crashes. This is a problem especially with global optimisers such as DifferentialEvolution when they sweep a large parameter space. Adding a callback function to the optimisers would allow us to handle these exceptions.

We need to decide on how to implement them, but in any case we should let the users implement their own if they choose so.

[PipGrylls]

Is this still a problem and if so can you provide an example

[brosaplanella]

Let's hold it for now, as this problem has not surfaced for a while so we don't have a specific example to use.