Call appropriate event for zombies igniting players. Adds BUKKIT-3915

### The Issue:
Currently, Zombies do not fire the appropriate EntityCombustByEntityEvent when igniting players.

### Justification for this PR:
As CraftBukkit has an event that is called in other places where entities are ignited by entities, it seems appropriate that they also fire this event here.

### PR Breakdown:
This PR adds the appropriate call to a new EntityCombustByEntity event when a zombie ignites a player.

### JIRA Ticket:
BUKKIT-3915 - https://bukkit.atlassian.net/browse/BUKKIT-3915