Explosions, TNT, Flint&Steel implementation

This is finished now, only missing things are:
- [ ] check whether the block is flammable (with Flint&Steel / by TNT)
- [ ] use the block's blast resistance

This requires values I'd prefer to be stored along with block's hardness, light level, and so on, so I'm waiting for the implementation of these to finish the things mentioned above.


Also please notice the survival bug I mentioned: #330 
There's another "bug" in GlowPlayer: A player's velocity won't be set to zero sometime, so if you add a velocity to a player it will stay there forever. Since an explosion "throws players away" by adding values to the player's velocity, the velocity will be higher and higher by every explosion.
That means the first explosion creates the right values for velocity, but after the second explosion the velocity will be double as high as normal, since the player keeps the velocity from the first explosion.
This won't be fixed in this PR, as it's a general bug in GlowEntity.

What's done:
- [x] add ItemType ItemFlintAndSteel
- [x] create explosions and drop the related blocks
- [x] setting blocks of explosions on fire
- [x] damage nearby entities [DONE, needs some implementation in GlowWorld]
- [x] set new velocity for affected entities
- [x] detect and fire near TNT
- [x] send explosion sound
- [x] send explosion particles
- [x] define and send explosion-packet (ExplosionMessage.java/ExplosionCodec.java)
From the wiki: `Its fuse lasts 40 redstone ticks (4 seconds/80 game ticks) if activated by redstone or fire, or a random number between 10 to 30 game ticks (.5 to 1.5 seconds) if it's destroyed by an explosion.` 

In other words, right here the number of ticks needs to somehow be passed down to the explosion objects (`setFuseTicks`). My recommendation is to add an overloaded method to `explodeBlock` that accepts a boolean: `blownUp` (name is just a suggestion). If that boolean is true, this 'random' tick count is applied, otherwise the standard is used. I would almost go as far to say that the boolean should further propagate to the explosion object that holds the fuse ticks so that magic numbers aren't all over the place.