[WIP] Quantile fallback for univariate distributions

The quantile can be inferred, e.g., from the cdf.

Open issues:
- how to handle unbounded DiscreteUnivariateDistribution
- default ``fzero`` throws ``PossibleExtremaReached(0.4983352449204162)`` exception for ``Kolmogorov( )``
- ``@checkquantile``does not work