[WIP] Improve entities

I'm working on completing the API for entities.
I need to do some research for the functions below, before adding, that's why I made a checklist.

- [x] Entities
 - [x] isOnFire()
   Every entity should be able to catch fire.

### Living Entities
- [ ] LivingEntity
  - [ ] getHeadHeight()
  - [ ] getFeetHeight()
  - [ ] getLivedTicks()
- [ ] Hostile
  - [ ] getTarget()
  Should we create an another interface for target with functions like getPlayer and getMob or let return it an   entity
- [ ] Witch
  - [ ] isDrinkingPotion()
  - [ ] getAttackState() ([States](http://minecraft.gamepedia.com/Witch#Behavior))
  - [ ] getDefenseState() ([States](http://minecraft.gamepedia.com/Witch#Behavior))
- [ ] Iron Golem
  - [x] hasRose()
  - [x] isAngry()
  - [ ] getTarget()
  - [ ] Utility Interface? ([Utility Mobs](http://minecraft.gamepedia.com/Mobs#Utility_mobs))
- [ ] Snow Golem
  - [ ] getTarget()
  - [ ] Utility Interface? ([Utility Mobs](http://minecraft.gamepedia.com/Mobs#Utility_mobs))
- [ ] Horses
  - [ ] getSpeed()
  - [ ] getJumpHeight()
  - [ ] Finish HorseVariant Interface
  - [ ] getArmor() 
    create an enum for horse armor?
- [ ] Wither
  - [ ] isCharging()

Some things are missing on this list, but i'm working on it