Add processor overlay display

[verhovsky]

A "?" icon in one of the corners, that when you mouse over it, it makes the processor a bit dimmer and overlays boxes around the different logical parts of it, like in the diagram on this page

https://sites.google.com/site/h2obsession/CBM/Hardware/6500-cpus

or more detailed like the diagram on this page

https://davidmjc.github.io/6502/bcd.svg

Like this:

[verhovsky]

In a similar vein, mousing over a register in the dropdown "MOS 6502" menu, should highlight just that register and ideally show where specifically each bit of the register is and its value. So if I highlight the Y register it would show something like