pcbgit v0.8.3

Updates no longer run as root, and a handful of everyday fixes.

• Service user: deploy/install.sh sets up a user (pcbgit by default) that owns the checkout, .env and /var/lib/pcbgit-control, and runs every update and check. Root keeps only the setup, the systemd units and Docker itself. The user is in the docker group, which amounts to root: this keeps the scripts' own work away from root, it is no wall. Existing servers move over by themselves on the update to this release. Commands by hand are now sudo -u pcbgit /opt/pcbgit/deploy/update.sh (plain sudo still works and switches user).
• Installer: numbered sections, colour, ✓ and ! for what it did and what to look at, and a summary at the end.
• STEP download as .step.tar.gz (board.step inside), sent as it is: the server no longer unpacks it for clients without gzip support. Versions rendered before keep their .step.gz, also sent packed, until re-rendered.
• Profile pages can be sorted (last updated, name, newest, stars) and page through more than 24 boards. An unknown sort in a link no longer gives an error page.
• Upload progress: uploading a ZIP (new board, new version) shows a progress bar. A ZIP dropped onto the drop zone on /new is now actually sent.
• Passwords: every password field has a show/hide button; new passwords are asked for twice at registration and when changing one.