blockColumn from attributes to child elements

same for blockRow
VectorSelectorSegmentType reshufeld

plus type relocated
MatrixColumnType removed for now
new MatrixRowCellType and

RowIndex for matrix rows added

- MatrixRowCellType is optional to Scalar/SymbRef/Sequence - the former
is indexed, the latter not
relaxed restrictions on matrix elemental building

blocks allowed to be used in matrix definition
2nd - sequence of rows/columns corrected
rows can be empty - but then defaults have to be defined