Environment cleanup

* Move client list to ServerEnvironment and use RemotePlayer members instead of Player
* ClientEnvironment only use setLocalPlayer to specify the current player
* Remove ClientEnvironment dead code on player list (in fact other players are CAO not Player objects)
* Drop LocalPlayer::getPlayer(xxx) functions which aren't used.
* Improve a little bit performance by using const ref list for ClientEnvironment::getPlayerNames() & Client::getConnectedPlayerNames()
* Drop isLocal() function from (Local)Player which is not needed anymore because of previous changes

This change permits to cleanup shared client list which is very old code.
ClientEnvironment doesn't use player list anymore, it only contains the local player, as addPlayer is only called from Client constructor client side.
Clients are only CAO on client side, this cleanup permit to remove confusion about player list.