EntityCoordinates are BlockCoordinates.

Everything starts with Coordinates. They have x, y and z.
Now FacingCoordinates adds pitch&yaw and BlockCoordinates add a world.
EntityCoordinates also adds a world, but is based on FacingCoordinates.
Conclusion: EntityCoordinates = FacingCoordinates + BlockCoordinates

This also cleans up the mutable interfaces a bit.
Merge pull request #7 from main--/ec-equals-bc

EntityCoordinates are BlockCoordinates.
Added ServerInterface.getPlayer(String)
Merge pull request #8 from main--/getplayer

Added ServerInterface.getPlayer(String)