Some optimizations

I figured out a reason to an FPS drop in 2D scenes (mainmenu/gameplay): The moving cloudy texture was generated by code -each frame- which was quite costly. Now the texture is generated only once and the movement is handled by a shader. I hope this brings FPS boost to anyone running the game with low-spec PCs (e.g. laptops).

At next, I think I need to have one more look to music/gfx sync as it still seems a bit off (or the time window for perfect/good is just too tight..)

Aand then I'll move to map some more songs. 

Take care,

Haru