Add APTv3 layout

[SmellyOrc]

Adds the APTv3 layout, described here, nothing more, nothing less :)

Tested locally, seems to work fine.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
packages/keybr-generators/layouts/en_aptv3.json	0% smaller
packages/keybr-generators/lib/generate-layouts.ts	0% smaller
packages/keybr-keyboard/lib/layout.ts	0% smaller
packages/keybr-keyboard/lib/layout/en_aptv3.ts	0% smaller
packages/keybr-keyboard/lib/load.ts	0% smaller

[aradzie]

Thanks!

[aradzie]

I will update the web site in a few hours.