operations: Add translated titles to operations

The GEGL Filter Browser and API-added
filters require a "title" attribute to be defined
in the operation in order for the filter
to have a name.
The GIMP custom GEGL operations do not
have a title defined, which causes display
issues in the browser and crashes when
attempting to edit API-created filters.

This patch adds "title" attributes for four
operations which are already translated.
The remainder will need to be added after
the string freeze is over for 3.4 development.

app/operations/gimpoperationbrightnesscontrast.c

@@ -61,6 +61,7 @@ gimp_operation_brightness_contrast_class_init (GimpOperationBrightnessContrastCl
 
   gegl_operation_class_set_keys (operation_class,
                                  "name",        "gimp:brightness-contrast",
+                                 "title",       _("Brightness-Contrast"),
                                  "categories",  "color",
                                  "description", _("Adjust brightness and contrast"),
                                  NULL);

app/operations/gimpoperationcurves.c

@@ -63,6 +63,7 @@ gimp_operation_curves_class_init (GimpOperationCurvesClass *klass)
 
   gegl_operation_class_set_keys (operation_class,
                                  "name",        "gimp:curves",
+                                 "title",       _("Curves"),
                                  "categories",  "color",
                                  "description", _("Adjust color curves"),
                                  NULL);

app/operations/gimpoperationlevels.c

@@ -60,6 +60,7 @@ gimp_operation_levels_class_init (GimpOperationLevelsClass *klass)
 
   gegl_operation_class_set_keys (operation_class,
                                  "name",        "gimp:levels",
+                                 "title",       _("Levels"),
                                  "categories",  "color",
                                  "description", _("Adjust color levels"),
                                  NULL);

app/operations/gimpoperationthreshold.c

@@ -85,6 +85,7 @@ gimp_operation_threshold_class_init (GimpOperationThresholdClass *klass)
 
   gegl_operation_class_set_keys (operation_class,
                                  "name",        "gimp:threshold",
+                                 "title",       _("Threshold"),
                                  "categories",  "color",
                                  "description", _("Reduce image to two colors using a threshold"),
                                  NULL);