It was explained to me that earlier Apple II models used the block
cursor, and only later ones used the checeked cursor. I try to never
underestimate the power of nostalgia, so let's have both.
This adds two new display modes to replace the old one. One is a
16-color mode and the other does TV "emulation" based on code in
AppleWin. Both of these modes should deliver more accurate colors,
including NTSC artifact colors.