Implement option for 1920x224 for uncalibrated sets

[xovox]

multiple users have complained that they're missing huge amounts of the screen on the top and bottom due to poor factory calibration

menu has been added to retrocrt_setup.sh, need to have it configured so everything that adjusts the resolution can read it and behave appropriately

• RetroCRT.yml
  • new math for retroarch.cfg files
• retrocrt_setup.sh
  • write /boot/retrocrt/retrocrt.txt
• scripts/runcommand-onstart.d/50-gen_ra_config.sh
  • new math to center the image
• scripts/runcommand-onend.d/99-set_screen_resolution.sh
  • not sure

[xovox]

the following consoles are > 224p and would be the only real obstacles to getting this done. therefore i'm creating a separate issue for these and pushing forward with 224p for the next release without them

atari5200
atari7800
msx
n64
pcengine
psx
sega 32x

[mukum5]

https://github.com/xovox/RetroCRT/issues/40#issuecomment-833455751