added using global levelset identifier and level number for network games

This change/addition was required for correctly handling identifiers
and level numbers when playing network games (for which the related
levelset possibly does not exist locally, but was sent by the network
server). This includes showing the correct level number for the level
that is played over the network, and saving the resulting high scores
for the correct level in the correct levelset score directory (again,
even if this levelset or level number does not exist locally).