Better Aspect Ratio

FPGABee's aspect ratio has always been a bit off - a bit squashed vertically:

To improve this, I've switched the VGA resolution from 640x480 to 800x600 and stretched it vertically to twice the height (scan line doubler). This looks a lot better:

I've also moved the PCU menu to the top right corner so it's less obstructive:

Games look better too:

Code Improvements

Also, I've done a bit of a clean up on the code:

• Extracted the core FPGABee functionality to a separate entity
• Wrapped the core in a new top-level entity specific to the Nexys3
• Remove all Core Generator components, including the clocking core and disk controller multiplier - these are all now inferred.
• Lots of other miscellaneous improvements.