addStuffToDiagonal method
void
addStuffToDiagonal()
Adding small boxed data-areas to DiagonalList. At the end this should be user - server -in-data stuff.
Implementation
void addStuffToDiagonal() {
// Using this method from tl, tools library.
// Problem is, that #matrix should be publicly visible.
// tl.boxInList(_r, _c, __l, _matrix);
}