Added the module.mk file for the scummvm backend
Added libAdventureEngine.a to the gitignore
Added a backends folder to the System folder

This is meant to store different backend implementation details.
Moved the Core folder into the System folder and updated all paths

This is done to once again provide a clean separation between the engine and
game logic. It also makes it really easy to find things as well.
Updated the scummvm module.mk to reflect the change in Core location
Added simple backend platform support
Added conditional execution for the makefile to allow different backends
Added a new makefile for the Backends directory
Added the Generic backend
Finished adding simple backend support
System/Core/usrsetup.h: Deleted the backend macros

I thought they would be necessary but it turned out they were not. Attempts to
use them would have resulted in a confusing mess maintenance wise