Base system accessibility wishlist

This includes documenting wherever appropriate accessibility-related changes made to the base system. Documentation-only changes go into Doc instead.

• Speech output support in vt(4): D35754 available for feature testing.
• Provide a VTY screenreader (which one?) in the installer itself, as self-configurable as possible, and that can be started on the initial menu with a simple key or key combination.
• Add a VTY screenreader (probably the same one) to the packages available from the installer so the installed OS can be speech-friendly from the first boot.
• Check the installer text and background colors provide enough contrast (including as shades of grey) and or offer options to change them.
• Document the accessibility options added to the installer and available for VTY-only systems.

• Screenreader support in the loader. (Earlier boot stages are probably unfeasible.)
• Speech recognition instead of a keyboard (that's a very tough one, maybe untractable - accents, spelling variants, ESL speakers, and I'm probably missing some).
• Other color schemes than white-on-blue (installer) or white-on-black (out-of-the-box default for VTYs), both configurable from the installer including for the installed OS.