Revamp the readonly installer?

[EternityForest]

I love the readonly script! But I think there's a few things that could be done to make it a little more bulletproof.

• A non-interactive installer. We should be able to script the whole process.

• A rename. Right now it does way more than just handle read-onlyness, so a new name might be in order to avoid confusion

• RTC integration? Fake-Hwclock is a disk write related thing

• Random seeding. Normally there's a thing that saves some entropy periodically so the pool is random from the moment you boot. I don't know if Linux does this automatically, but if not, we should seen urandom with some entropy from the HWRNG at boot.

• NTP Integration, don't set the clock if NTP or Chrony isn't synced, and make sure the drift correction stuff still works. Also, install NTP if the user hasn't chosen chrony, because timesyncd isn't that great IIRC

• Keep logrotate, just give it a tmpfs state dir.

• A mode to make things kinda-sorta-fake-read only, where we still put everything unnecesary in a tmpfs. This means you can use the script on a "normal" pi that isn't an embedded system. From experience, a pi will be fine running almost 24/7 for years this way, and the chances of corruption are lower than stock.

I have an experimental version here with most(Almost all, except the default not-actually-read-only mode) of the features untested that implements these. I have some RTCs in the mail to test that though.

Not sure which are really needed, but it seems that such a central script to a lot of use cases could stand a few tweaks.

https://github.com/EternityForest/scripts/tree/master/embedtools