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.

core/dr-catalog/src/rating.rs

@@ -814,7 +814,10 @@ mod tests {
         assert!(all
             .iter()
             .all(|id| found[id].label == Some(ColourLabel::Blue)));
-        assert_eq!(label_histogram(cat.connection()).unwrap(), [0, 0, 0, 0, 4, 0]);
+        assert_eq!(
+            label_histogram(cat.connection()).unwrap(),
+            [0, 0, 0, 0, 4, 0]
+        );
     }
 
     #[test]

core/dr-types/src/place.rs

@@ -135,6 +135,10 @@ pub struct StoredFilter {
     /// Travels: it is a narrowing like `local_only`, and a record without it
     /// — from a build before it existed — reads as off.
     pub eyes_open: bool,
+    /// TRACES: FR-CAT-6
+    /// The colour label the grid was narrowed to. A record without it reads
+    /// as none, as every term added after the first does.
+    pub label: Option<crate::ColourLabel>,
 }
 
 /// Where the photographer was, at the moment they were there.