Quick copy "disk folders" mode, file grouping, configurable EXIF fields and natural sort fix

[bitblaster]

Four improvements, built on top of each other:

1. "Disk folders" mode for the quick copy/move panel

Pressing 0 now toggles the panel between the configured shortcut folders
(1-9) and the first 9 subfolders of the current image's directory, so files
can be quickly filed into siblings of the folder being viewed without
preconfiguring them. The last used mode is remembered across restarts.
Also fixes a latent bug in MenuItem where its internal QHBoxLayout was
a plain member handed to setLayout(), which expects a heap-allocated
layout it can delete itself — this only surfaced now that CopyOverlay
rebuilds its row widgets at runtime instead of just once at construction.

2. Group files sharing a base name (e.g. RAW+JPEG+XMP) into a single entry

Adds an opt-in "grouping" mode (Settings → General) that collapses files
with the same base name but different extensions (RAW+JPEG pairs, XMP
sidecars, etc.) into one directory entry, picking a representative file by
a configurable extension priority list.
File operations (rename, move,
copy, delete) performed on the representative are applied to every file in
the group, and the UI (title bar, thumbnails) shows a "+ ext + ext" suffix
for grouped entries.

3. Configurable EXIF info fields, prefer DateTimeOriginal

Preferences → View now has an EXIF info fields table (checkboxes + move
up/down) to choose which EXIF tags are shown in the image info panel and in what order, instead of the previous fixed alphabetical list.
Extracts several additional fields (lens ID/range, exposure compensation,
computed light value, focus mode, orientation, GPS position, software) and
prefers DateTimeOriginal/DateTimeDigitized over the file-modification
DateTime tag.
The info overlay's name column now sizes itself to the
widest rendered label, values wrap instead of being clipped, and the
overlay is no longer capped at a fixed width, since the new labels/values
are often longer than before.

4. Fix natural sort order to match most file managers (e.g. Dolphin)

QCollator's locale-aware (ICU) collation weighs punctuation in ways that
don't match plain ASCII order, and can rank _ below . or even below
digits. Comparing a full "name+extension" string in one go could therefore
place e.g. photo_01.tif before photo.jpg, or img_2013.jpg before
img006.jpg, unlike most file managers.

Splitting the extension off before comparing (the same approach used by
Dolphin's KFileItemModel) avoids ever comparing . against _ or a digit
in these cases, restoring the expected natural-sort ordering.