[BUG] Delete sprite in "sprite window" won't delete it on frames using it

[dtatane]

When you delete a sprite from the sprite window, it is not deleted in the frames that are using it.
Perhaps it's not a big issue when running the colorization..

It would be better to :

• detect if the sprite is used on frames
• ask for confirmation if it used already
• delete it from the sprite list of the frames that were using it

[zesinger]

I start to work on it

[zesinger]

fixed