Optimize network traffic a bit: - Send keepalive packets every second - Don't send keepalive packet if there was action packet within a second Time between turns in net game is reduced to 1 second now (was 2 seconds)

foreach(dir "Fonts" "Forts" "Graphics" "Locale" "Maps" "Music" "Sounds" "Themes" "Trainings" "Names")
  add_subdirectory(${dir})
endforeach(dir)