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_arrowtarget.h

@@ -0,0 +1,11 @@
+#ifndef SERVER_ARROWTARGET_H
+#define SERVER_ARROWTARGET_H
+
+#include <QObject>
+
+class Server_ArrowTarget : public QObject
+{
+    Q_OBJECT
+};
+
+#endif