Added proxy support (fixes #114). Thanks @Johni0702!

Proxies such as BungeeCord have the option to forward the real address,
UUID, and properties from the auth process to the backing server so that
they can appear to be in online mode even if they are not.
Added item FlintAndSteel
added TNT/explosions
Explosion: drop blocks, set them on fire, fire events
use BlockVector
entity damage
added ItemTool for easier damage handling; formatting; yield for explosions
some start for ExplosionPacket
use constant Explosion.POWER_TNT instead of value 4
added EntityStorage TNTPrimedStorage
particles, sounds, bug fixes and improvements
bug fix: use Particle.SMOKE instead of Effect.SMOKE