Implement basic block physics

This commit includes the ability for the server to demonstrate basic block
physics as described below. This provides a base for many other future
commits for things like neighbor updates and other missed physics cases.

This commit adds the following physics cases:
- Falling blocks (sand, gravel, anvil, and dragon egg)
- Tower blocks (cacti and sugar cane)
- Attached blocks (carpet, dead bushes, fire, melon stem, pumpkin stem,
  snow, tall grass, and torch (redstone & otherwise))
Add bare bone implementations for some Entities
Implement resource pack event and methods for 1.8

This commit implements the event for the client reporting the status of
the application of a resource pack after it has been sent. This event may
be fired with illogical statuses due to bugs in the client's operations.

This also adds the applicable methods for plugins to set a specific
player's resource pack, or at least prompt them to, using the newly
implemented identifier system.