Sourcegrandaverage should also average the anatomy (when present)

[robertoostenveld]

@henneysq is working on a script with 1. ft_sourceinterpolate and 2. ft_volumenormalise, followed by 3. ft_sourcegrandaverage. We identified that after 1 and 2 the anatomy is there, but after 3 not. And ft_sourcegrandaverage does not support a cell-array for cfg.parameter.

We can extend ft_sourcegrandaverage to support a cell-array, or perhaps to have it automatically average the anatomy (ignoring the inside).

[robertoostenveld]

Another observation is that ft_sourcegrandaverage returns the averaged data (pow, anatomy, inside) as vectors rather than volumes,

[robertoostenveld]

I recall that some of the FT main functions that work on source and/or volume data make use of private/parameterselection.m, and some not. Looking for that function may help to identify those functions that can work on one input parameter (like pow) or on multiple.

Regarding the vectors versus 3d arrays in the output: perhaps we can use something similar to the israw/istimelock that we have in other functions for reformatting the output to a representation that is consistent with the input.