Add support for double hi-res

[fadden]

Add support for double hi-res graphics. This presents a few challenges:

• Color is 140x192, monochrome is 560x192. We need to use 560x384 and treat pixels as 4x2 when in color mode.
• Showing color pixels as solid colors isn't quite right. The output on an Apple IIgs RGB monitor looks very different, and the output on an Apple //e looks even more different. We may need a way to toggle the display to show a closer approximation.
• We need a new set of dither patterns. For consistency, the palette from the 1984 release of The Graphics Magician is the best candidate.
• Copying & pasting between screens of different types requires a conversion step.

[badvision]

The NTSC pull request I submitted has the start of this; the NTSC mode uses 560 width, but still has the 280 width and grid overlaid when editing. I didn't change mono to do something similar for half-bit shift, wasn't sure if you wanted mono to stay as-is or not.