Bugfix firstround selection algorithm

There was a double adding of the own distance if the firstround host
and a missing sort for distance after erasing duplicates.

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Hide firstround candidate struct in the cpp file

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Add a simple unittest for Forstround selection

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Enable unittest for Firstround_selection

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>