JonkerVolgenantAlgorithmSparse: add a constructor.

Signed-off-by: Jean-Yves Tinevez <jeanyves.tinevez@gmail.com>
Test for the JonkerVolgenantAlgorithmSparse.

It's all well and nice, it finds the same results as the non sparse
version (which finds the same results as the Munkres algo), but GOD it
is slow. It is about 10 to 20 times slower than the non-sparse version.
Needs more engineering.
Signed-off-by: Jean-Yves Tinevez <jeanyves.tinevez@gmail.com>