calendar-button: Bind calendar color with paintable

When updating the color of the calendar, the corresponding colored dot
in the "Calendars" popover does not change. This is due to the fact that
GListModel doesn't notify when one child changes internally. Any widget
depicting a calendar should watch for changes on the data.

To fix this, I used the same code as in GcalEventEditorDialog, which
creates a binding between the calendar's color and the paintable inside
the image.

src/gui/gcal-calendar-button.c

@@ -50,6 +50,17 @@ static GParamSpec *properties [N_PROPS];
  * Auxiliary methods
  */
 
+static gboolean
+paintable_from_gdk_rgb (GBinding     *binding,
+                        const GValue *from_value,
+                        GValue       *to_value,
+                        gpointer      user_data)
+{
+  GdkRGBA *rgba = g_value_get_boxed (from_value);
+  g_value_take_object (to_value, get_circle_paintable_from_color (rgba, 16));
+  return TRUE;
+}
+
 static GtkWidget*
 create_row_func (gpointer data,
                  gpointer user_data)
@@ -57,7 +68,6 @@ create_row_func (gpointer data,
   g_autoptr (GdkPaintable) paintable = NULL;
   GcalCalendar *calendar;
   GtkWidget *label, *icon, *checkbox, *box, *row;
-  const GdkRGBA *color;
 
   calendar = GCAL_CALENDAR (data);
 
@@ -71,11 +81,16 @@ create_row_func (gpointer data,
   gtk_widget_set_margin_end (box, 6);
 
   /* source color icon */
-  color = gcal_calendar_get_color (calendar);
-  paintable = get_circle_paintable_from_color (color, 16);
-  icon = gtk_image_new_from_paintable (paintable);
-
+  icon = gtk_image_new ();
   gtk_widget_add_css_class (icon, "calendar-color-image");
+  g_object_bind_property_full (calendar, "color",
+                               icon, "paintable",
+                               G_BINDING_DEFAULT | G_BINDING_SYNC_CREATE,
+                               paintable_from_gdk_rgb,
+                               NULL,
+                               NULL,
+                               NULL);
+
 
   /* source name label */
   label = gtk_label_new (gcal_calendar_get_name (calendar));