ACCESS: Support for Amazon - Guardians of Eden

This is a pull request for the game Amazon - Guardians of English. It uses the Access engine, which was used for several games, so it may well end up supporting more games in the future. Currently, it supports both the floppy and CD versions, as well as the demo. The game is completable, although further gameplay testing is required. There are only a few things left to do for the game:
* Some polishing of the sound/music/voice playback code.
* Dirty rect list isn't enabled yet. The game has a dirty rect list, but it's not yet being used.
* There are a couple of spots in the game that the original implements things in a way that I'd consider to be bugs, that I'd prefer fixing under ScummVM.

Source-wise, the code is pretty solid, with everything already nicely re-factored into separate classes for the various parts of the engine, and we've already spent some effort to keep Amazon game specific code separate from the core engine, so hopefully it won't be too hard to add support for further games in the near future.

Making GET_MESSAGE etc. "const char foo[]" makes this warning go away, so probably a good idea to use.