accessibility improvements, memtest86+, bootloader menu improvements

[classabbyamp]

bootloader improvements:

• mklive: add memtest86+ to images
  • closes #346
• isolinux: add menu entries for screenreader, memtest, reboot, poweroff
• grub: add menu entries for screenreader, memtest, efi fw setup, reboot, poweroff

a11y improvements:

• dracut/vmklive: rename live.screenreader to live.accessibility
• build-x86-images.sh: add void-live-audio for a11y audio setup
• build-x86-images, dracut/vmklive, installer: add support for brltty
• build-x86-images: add orca, graphical screenreader
• closes #345

misc:

• build-x86-images: remove duplicate line
• build-x86-images.sh: switch to pipewire on non-base images
  • closes #301

[classabbyamp]

test images for this and #349: https://devspace.voidlinux.org/abby/live/mklive-349/