Extend monkeybread neighbourhood to include n>1 cells

[timtreis]

Just discussed with @maiiashulman. Would be great to extend the monkeybread nhood niche def method to include a "distance" parameter. Default is 1 = closest touching cell, could extend to > 1 with weights.

[LLehner]

@timtreis Where exactly would this be applied (and why)? Before calculating the niches you need to calculate the spatial neighborhood graph, where you already decide on how many neighbors you want to include. Also why is it restricted to this one approach when essentially all methods we implemented make use of the neighborhood?