row or column based direct summands?

[kalmarek]

@blegat
I think we just happen to do it row-based by a historical accident now (row_echelon_form). I think all of this should be rewritten to column_echelon_form anyway, but this is just internals; users will face row-based symmetry_adapted_basis I think it should be changed to column-based. Any objections?

[blegat]

I use the fact that the output is in row-echelon here: https://github.com/jump-dev/SumOfSquares.jl/blob/master/src/Certificate/Symmetry/wedderburn.jl#L111
However, if it's just internal and the users get a row-based one I have no objection