Cut unnecessary connections between LevelControl, ChunkFactory and LevelChunk

Previously LevelChunk needed to know its designated parent from the
start, which meant that LevelControl created a LevelChunk and sent it
to ChunkFactory. Now ChunkFactory actually creates the LevelChunk, and
the LevelChunk doesn't get to know its parent node until right when
it's about to be attached to it.
Chunks split into static and moving objects

The ChunkFactory now places a LevelChunk, with all static objects, in a
list together with all moving objects. LevelControl can then keep them
separate, and during update() check if a moving object has moved too
far left and remove it, separate from the same check on the static
chunks.