Added flag to disable the fade-in effect

Hi Nick,
I found out a problem with iCarousel and FXImageView, due to the two fade-in animations on iCarousel and FXImageView starting at the same time and conflicting each other.

I added a new flag to disable the fade-in effect on FXImageView.
I set it to be enabled by default so to keep the code 100% backward compatible.

Cheers,
Andrea