v0.54.0

The rest of the issues from the 10 October review: 80 fixes, each with a
test. Nine findings that change behaviour or are features in themselves were
left for a decision (RAW auto-brightness, time zones of videos, 16-bit
export, export metadata, more formats and others).

Changed

• The window stays responsive: making thumbnails after an import,
  removing a source, setting one duplicate group aside, counting smart
  albums and reading a folder for import (which can now be stopped) run in
  the background.
• A photo opens from any page - People, On this day, a frame in the
  stack tray - even when the Library is filtered; Back says where it goes.
• Tags, face names and edits reach their sidecars a moment after you
  make them, as ratings do, not at the next restart.
• Faces and folder jobs are faster: known faces are read once per pass,
  and each folder's files are found through the index instead of listing
  the whole source.
• The family gallery prefers your home network over a VPN adapter, opens
  the catalog once per request, and never keeps PIN or error pages in the
  browser.
• Thumbnail memory is capped by size (about 400 MB for the grid), not by
  count.
• Catalog: indexes that make removing files quick after a migration;
  the newest five pre-upgrade backups are kept instead of all of them.

Fixed

• Sidecars: one with no rating cleared the photo's stars; keywords
  added in another program could be overwritten. Sidecars are flushed to
  disk before they replace the old one.
• Import: a full library drive pauses the import with a message instead
  of failing every remaining file; evening imports were filed under
  tomorrow's date.
• A passing read problem (a file open elsewhere, memory short for a
  moment) made a photo "preview unavailable" or "no metadata" for good; it
  is tried again on the next passes.
• Exports: above ISO 65,535 failed with metadata on; a cancelled or
  crashed export left a half-written file under its final name.
• Duplicates: a copy is not set aside unless the one being kept is
  still on disk; verifying several groups in a row skipped the middle ones;
  emptying the quarantine could remove another file's sidecar.
• Selection and keys: Ctrl+A in the photo view selected the hidden
  grid; S, rating keys and Copy edit settings acted on a different photo
  from the one on screen in several cases.
• Migration: a damage flag you dismissed still counted.
• The same folder could be added twice, as a drive letter and as a
  network path.
• 16-bit greyscale scans came out white; smart-album shutter rules
  misread some speeds, and one malformed rule broke the Albums page.
• Start-up: a bad backup zip chosen for restore crashed the next start.
• Updates: a newer test version was not offered over an older one.
• Plus smaller fixes: messages that vanished before they could be read,
  icons that kept the old theme's colour, the Takeout tree collapsing on a
  filter change, People lists jumping to the top, the tray icon always
  switching to the Library, "No" to "Quit anyway?" not being respected.