pass current engine version to every download for future dynamic responding and backward compat.
add prerequisite check
rearrange things a little
move background image management to dedicated class
revamp layer (z-index)
rename SongDisplayManager to DynamicBackground
change screen method ordeing to onIn -> tick -> handleKey -> onOut
add basic song info to dynamicbackground
fix minor stuff in screen code + make cheat enterable in presong screen
add global overlay to prevent accidental text selection