Moved get_cluster and add_cluster to use _write_file and _read_file.
Changed add_player() to use save_object().
Removed unused Database methods.
Changed add_cluster() to use save_object() method for writing the .cluster file.

I tested this by adding a beta cluster, which wrote successfully, but I removed it for now.
Changed add_sector() to use save_object().
Changed add_planet() to use save_object().

In testing this, I found some issues with creating a home sector and planet, which I resolved in Game.
Fixed an error on page load when the player is not in the database.
Merge pull request #7 from ChodeGames/code_cleanup

Code cleanup