Issue #12146: default to HSV Hue for GimpColorSelect.

Commit abf0c1c fixed the inconsistency of showing "R" for RGB's Red
channel selected whereas the actually displayed selection UI was "H" for
HSV's Hue channel.
As a consequence of this fix, now we were indeed displayed "R". Yet
people got used to working with the Hue channel (and LC plane) for
at least a dozen years. Let's make "H" the officially displayed channel.

app/widgets/gimpcoloreditor.c

@@ -198,7 +198,7 @@ gimp_color_editor_init (GimpColorEditor *editor)
 
   color = gegl_color_new ("black");
   editor->notebook = gimp_color_selector_new (GIMP_TYPE_COLOR_NOTEBOOK, color,
-                                              GIMP_COLOR_SELECTOR_RED);
+                                              GIMP_COLOR_SELECTOR_HUE);
   g_object_unref (color);
   gimp_color_selector_set_show_alpha (GIMP_COLOR_SELECTOR (editor->notebook),
                                       FALSE);

libgimpwidgets/gimpcolorselection.c

@@ -187,7 +187,7 @@ gimp_color_selection_init (GimpColorSelection *selection)
                                   GTK_ORIENTATION_VERTICAL);
 
   priv->color   = gegl_color_new ("black");
-  priv->channel = GIMP_COLOR_SELECTOR_RED;
+  priv->channel = GIMP_COLOR_SELECTOR_HUE;
 
   main_hbox = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 6);
   gtk_box_pack_start (GTK_BOX (selection), main_hbox, TRUE, TRUE, 0);