Remove currently obsolete shell files.

Add:
	src/interpreter/(shell, shell_graphics).(c, h)
		-Remove all of the engine's interactive shell source, which is currently
		entirely incompatible with MDL and, thus, obsolete.
		-Will be reimplemented with MDL support at a later point, time
		permitting.

	src/interpreter/(file_parser, interpreter).c
		-Remove commands used for parsing files and commands in the engine's old
		scripting language.