Redstone framework

This is just the start of a redstone framework which actually ended up being somewhat different from the initial prototype.

This is for issue #116 Redstone Support. I have dropped the WIP tag as I am satisfied that I have a suitable working subset of RS functionality (even though the torch timing is 1-tick rather than 2-tick).

Current status:
* **DONE** - RSManager class tied to world to handle the redstone network
* **DONE** - Chunks are dirtied, updated and unloaded by GlowWorld and GlowChunk
* **DONE** - pulse() method hooked up to GlowWorld
* **DONE** - Actually load chunk data into RSManager
* **DONE** - Redstone torch blocks
* **DONE** - Basic redstone logic
  * **DONE** - Redstone torch->solid->torch sequence
  * **DONE** - Redstone wires - diagonals ARE blocked, and these ARE analogue! (NEW: "injection" and charging of solids)
* **FIXED ITSELF?!** - Actually relay redstone updates to client (should be there BUT there's some stupid bug somewhere which is preventing this from actually working)
* **DONE** - Prevent placement of redstone dust ("wires") on a lot of things (mostly RS dust, RS torches)

To be implemented in later pull requests:
* Actually deregister chunks properly
* Faster deregistering of chunks
* Proper network creation which doesn't require tracing wires every pulse (prototype uses HashSets to mark positions of "sources", torches, and charged wires - it's not going to hit *every* block each frame!)
* Repeaters
* Comparators

This getdrops will return the same value as the base class, no usage for it here. Setdrop isn't useful either for this particular item. It might be useful in the Redstone torch class so you don't accidently give the user an unlit redstone torch. But this is the torch class.