On-device installer

We need an on-device installer! Why? Because we have pre-built images (https://images.postmarketos.org) which at the moment have a hardcoded username and password, a set disk size (which people are currently manually resizing using external tools) and no full-disk encryption.

I was thinking of trying to use Calamares for this. tl;dr: it's a distribution independent system installer. It already has the option to do everything I've mentioned above, so there is no need to reinvent the wheel. I have already done some work on making this available in Alpine a while ago, which I have pushed my changes for here.

I'm not sure if it's mobile-friendly at the moment (read: responsive UI and touch input capable), but I think it's less to work to make it so rather than creating our own thing.