Clustering prechecks

[aretaon]

Migrated from Gitea

In #2 a

submodule that checks if an object is usable for a certain kind of clustering

was requested.
So far, both HCA and KMeans require plain MxN numpy arrays without NaNs as input. This is checked in the init procedure.
This needs further clarification.

[aretaon]

As stated in the documentation (https://docs.scipy.org/doc/scipy/reference/generated/scipy.cluster.hierarchy.linkage.html) not all "linkage" models work with every "methode" (see Note 2.). The same is true for the kMeans clustering. So the question is if we include some warning for certain combinations.

The same question is true for other functions which rely on data transformation (e.g. vsn works only with log transformed values).