Add HUD flashing animation types to config

[aleksandarbst]

The timing of the flashing when showing predicted hearts and food feels a little slow for me.
Could this be extended to offer a preset to switch between the current easing, and no easing between 0 and 100 opacity/alpha? And for more control, a config for the timing as well, eg interval between 0 and 100 opacity/alpha. This is just personal taste control, not high priority at all