Rename tipping_probabilities to basin_overlap

[Datseris]

Tipping probabilities is such a missleading function name... A function should be named accoring to what it does / what it gives you. And what this function gives you is super simple: the overlap of some basins of attraction before and after some change. Whether this can be interpreted as a "tipping probability" or not is subjective and up to the using scientist to decide.

We should rename the function objectively and accurately according to what it does.