Add interface for InverseCumulativeDistribution method

[TheSentry]

I'm implementing Copulas in my project and need to use the InverseCumulativeDistribution method during integration. I want to be able to construct that Copula using arbitrary continuous univariate distributions, but the existing interfaces do not include double InverseCumulativeDistribution( double p ), probably because not all distributions have those.

It would be nice to have an interface, e.g. called IInvertibleContinuousDistribution, that defines that method so I can implement my scenario with the proper abstraction.
This could also help the related issue about #434 "Missing InverseCumulativeDistribution support"

If this idea meets positive resonance, I'm also willing to make a pull request for it.