Add chunks.

Chunks are little extracts of the game world, each containing a limited
amount of blocks. With this technique, not the whole world has to be
loaded into memory, but just little chunks of it.
Add equals and hashCode functions to most classes.

These classes are:
- BlockDirector (also add documentation for getBlock method)
- GenericBlock
- GameCoordinate
- ImageExtract
- MonitorExtract
- TilePackage
- World
Add test class for Chunk

This also includes adding the junit dependency to the pom.xml file.