Distinct Leader Zombies

Now that leader zombies spawn properly now (after 12 years might i add), I thought it would be interesting and helpful to make them have visual distinction.

Instead of not knowing if a zombie will have more health than normal, this pack makes it obvious if it is a leader.

REQUIRES ETF/OPTIFINE

(note: since neither ETF nor optifine are updated to the most recent snapshot, it will not work in the current update)