Revert "Deleted unnecessary files."

This reverts commit 953bf8e694ff46d975763aba3a1166986a09c5c4.
MAJOR OBJECT CHANGES

Removed entities folder. Merged Entity and Mob class files and created
Thing file. Modified Player class to extend Thing.

Created AllThings class that organizes and keeps track of all the
objects together (Thing and Player classes). These changes are in a new
package called things.

Modified Game file to compensate for these things.