Corrected very important comment about assigning steps to bins

Points (and steps) are assigned to bins currently by their point of origin as is now correctly clarified by the comments.
Implemented compiledSelectByMiddlePoint

Given a set of points it returns all steps whose middle point belongs to the bin.
TODO: implement stride
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Select by middle point works, but has problems with periodc conditions.
GetDiffusionInBinByMiddlePoint works!