Forced bogomem_size to 0 by default, added A1200 model without extra memory, updated README accordingly
Created by: sonninnos
This extra model allows Second Samurai AGA to work.
Also changed the pecking order of the filename detection to check A1200 models first, then A600 and then A500 models.
And since the UAE built in model prefs are never used with this core, I defaulted bogomem to 0. Otherwise A1200 would have bogomem, and that is no bueno.