rebin does not conserve counts for factor < 1

[fzeiser]

rebin does not conserve counts for factor < 1

>>> a = om.Vector(values=[2,3], E=[4,5])
>>> b = a.rebin(factor=1/4, inplace=False)
>>> a.values.sum()
5.0
>>> b.values.sum()
2.8571428571428648

whereas it works as expected for factor > 1:

>>> c = b.rebin(factor=4, inplace=False)
>>> c.values.sum()
2.857142857142864

[fzeiser]

I don't think that this is ever used in the code as it is right now, but should be fixed for later