Re-base some of this project on the official pi-gen tool

[pmansour]

I recently discovered https://github.com/RPi-Distro/pi-gen, self-described as a "Tool used to create the raspberrypi.org Raspbian images". I believe this is used to generate the original distro image files which the current download-img.sh file downloads and the prep-img.sh file modifies.

Instead of downloading the prebuilt image and modifying it in several different places (some static, some at runtime), it might be better to just fork that repo and tune it to work for this use-case.

Some benefits are:

• Almost all configuration, including package installs, can be done statically, rather than on first-boot.
• Don't need to download a ~2-3GB base image initially.
• Use a maintained official tool, instead of writing/maintaining my own.
• Built-in support for a config file, instead of interactive shell parameters.

A secondary benefit here is that they include some functionality to build this in a docker container (to emulate an arm architecture for some of the runtime pieces). It would be interesting to study this build container image and see if I can learn enough to produce a lightweight image that just contains chromium + the chrome extension.