Update 1.996 Patchnotes

[nidefawl]

- Added missing bird textures
- Tweaked the weight of some enchantments, it should be easier to get high-level ones now
- Tweaked aether spawns a little
- Tweaked block ticks to reduce lag, stuff may grow slower now
- Re-Added automatic killing of too much mobs/entitites in one area
- Throttled block update packets to reduce lag on client and server
- Throttled chest update packets to reduce lag when there are lots of chests in one area