Added EntityMinecartTNT for diff visibility.
[B+C] Implemented interface FusedExplosive. Fixes BUKKIT-3962

Implemented the interface for TNTPrimed, TNTMinecart and Creepers.

For Creepers, the way the fuse ticks worked had to be changed for consistency.
Before, it went from 0 to the maximum, whereas now it goes from the maximum to
0, as for TNTPrimed or TNTMinecart. This allows the setFuseTicks to be exactly
the number of ticks before the entity explodes in all cases.
Added ExplosionPrimeEvent for TNTMinecart
Cleaned up the access, renamed fire to isIncendiary.
Corrected the implementation of yield to respect the radius feature.
Renamed the Creeper's fire field to isIncendiary
Remove the field yield, duplicating the explosionRadius. Correct the use of explosion radius and save it to NBT.
Store the incendiary status in NBT tags.
Added comment about the radius resetting of the setPowered method.
Corrected NBT tag name.
Added NBTTag information saving/loading for MinecartTNT and TNTPrimed
Added implementation of the ExplosiveFuseStartEvent for Creepers and
MinecartTNT