Renable cso

I've renabled custom content. 

Alas it doesn't work quite correct. I have managed to get most of the unpacking code working but it ends up writing to a new file. To be able to write to files we will need to reverse the swayer_encoding. I'm sure it wouldn't be too hard to do but I've used up all my energy for now. At least now you will get a little error message when it fails informing you to run the file once in vanilla rct2. I tried to use a callproc to get it working but I've re-arranged too many of the global variables and I can't work out which one causes it to crash.

Another note. If any file is corrupt or missing the game will crash with no useful error message.