Show and set colour labels in the grid and develop, and filter by them

Colour labels could be read from a Lightroom sidecar and queried by the
selector, but nothing drew one or set one, so the only labels a library
held were ones another program had written.

Every mark carries its label's initial on its colour — R, Y, G, B, P —
so a label is read without telling red from green, which is what
NFR-A11Y-3 asks of colour labels by name. A grid cell shows the mark
before its filename. In the grid, 6, 7, 8 and 9 set red, yellow, green and
blue as Lightroom's keys do, on the photograph under the pointer or on
the selection by the rule the star keys follow; the same key again takes
the label off, and over a mixed selection it sets it on all. The
selection bar gains Label, which opens the six choices — each a mark and
a name — and purple, which has no key, is there. In develop the top bar
says "Label: Green" beside the mark, opens the same choices, and 6-9
label the open photograph.

Each gesture is one catalog transaction, then the grid, the counts and
both sidecars are written as a rating's are. The filter bar gains a chip
per label, its mark and its name with a count, one at a time; the filter
is one SQL term, travels in the place record, and "All" clears it.

ui/dr-ui/src/library_ui/window.rs

@@ -19,7 +19,7 @@ use crate::{AppWindow, Library, LibraryCell};
 use super::controller::{stop, LibraryController, LibraryFacts};
 use super::filter_bar::period_headings;
 use super::offline::{collection_images, refresh_offline, scope_is_pinned};
-use super::ratings_keywords::{refresh_rating_counts, sync_ratings};
+use super::ratings_keywords::{refresh_label_counts, refresh_rating_counts, sync_ratings};
 use super::sync::start_sweep;
 use super::timeline::{civil_from_unix, format_date, refresh_timeline, restore_position};
 
@@ -367,6 +367,7 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
                 // window, not one per cell.
                 rating: 0,
                 flag: 0,
+                label: 0,
                 // And by `bursts::sync_badges`, in one more query for the
                 // window. Zero is "not in a burst", which is what almost every
                 // photograph in a library is.
@@ -424,6 +425,7 @@ pub(super) fn load_window(window: &AppWindow, ctl: &Rc<LibraryController>) {
     // so a cull still watches its own chips move.
     if describes_something_new {
         refresh_rating_counts(window, catalog);
+        refresh_label_counts(window, catalog);
     }
 
     // The library got shorter while the view was looking at it — a delete.