squash #6156 (#6161)

* move common server files

* update includes with move

* create participant, move code

* fix linker errors

* fix regressions

* mark function as override to make clang happy

* split out spectator to new file

* forgot to add to cmakelists

* autocompleter picking wrong casing for var name

* clean up forwards declarations in player

* fix includes in game

common/server/game/server_spectator.cpp

@@ -0,0 +1,11 @@
+#include "server_spectator.h"
+
+Server_Spectator::Server_Spectator(Server_Game *_game,
+                                   int _playerId,
+                                   const ServerInfo_User &_userInfo,
+                                   bool _judge,
+                                   Server_AbstractUserInterface *_userInterface)
+    : Server_AbstractParticipant(_game, _playerId, _userInfo, _judge, _userInterface)
+{
+    spectator = true;
+}