First attempt at implementing an Allocation pool

Now we just need to work out what to do in the three callbacks
depends on #951
Bad formatting. Either put all of this on a single line, or like this:
```cpp
cChunkMap::cChunkLayer::cChunkLayer(
	int a_LayerX, int a_LayerZ,
	cChunkMap * a_Parent,
	cAllocationPool<cChunkData::sChunkSection> & a_Pool
)
```
Never ever use spaces at the start of a line, always a single tab indent level.