[WIP] Explosions (and TNT)

This is WIP now, so I'd appreciate some feedback.

What works / what to do:

- [x] create explosions and drop the related blocks [DONE]
- [ ] use the block's blast resistance [TODO]
- [x] setting near blocks in fire [DONE, but see below]
- [ ] check whether they are flammable [TODO]
- [x] damage nearby entities [DONE, needs some implementation in GlowWorld]
- [x] detect and fire near TNT [DONE]
- [x] send explosion sound [DONE]
- [ ] send explosion particles [TODO, needs addings in GlowWorld]
Probably a bit much white space here ;)