particle: add an 'on_click_template' to base constructor.

This is intended to be a format-like string, with the possibility to
use tag formatters.

The expanded string will later be passed to the system() call.

particles/empty.c

@@ -30,7 +30,7 @@ instantiate(const struct particle *particle, const struct tag_set *tags)
 struct particle *
 particle_empty_new(int left_margin, int right_margin)
 {
-    struct particle *particle = particle_common_new(left_margin, right_margin);
+    struct particle *particle = particle_common_new(left_margin, right_margin, NULL);
     particle->destroy = &particle_default_destroy;
     particle->instantiate = &instantiate;
     return particle;

particles/list.c

@@ -123,7 +123,7 @@ particle_list_new(
     for (size_t i = 0; i < count; i++)
         p->particles[i] = particles[i];
 
-    struct particle *particle = particle_common_new(left_margin, right_margin);
+    struct particle *particle = particle_common_new(left_margin, right_margin, NULL);
 
     particle->private = p;
     particle->destroy = &particle_destroy;

particles/map.c

@@ -60,7 +60,7 @@ struct particle *
 particle_map_new(const char *tag, const struct particle_map *particle_map,
                  size_t count, struct particle *default_particle)
 {
-    struct particle *particle = particle_common_new(0, 0);
+    struct particle *particle = particle_common_new(0, 0, NULL);
     particle->destroy = &particle_destroy;
     particle->instantiate = &instantiate;
 

particles/progress_bar.c

@@ -175,7 +175,7 @@ particle_progress_bar_new(const char *tag, int width,
     priv->empty = empty;
     priv->indicator = indicator;
 
-    struct particle *particle = particle_common_new(left_margin, right_margin);
+    struct particle *particle = particle_common_new(left_margin, right_margin, NULL);
     particle->private = priv;
     particle->destroy = &particle_destroy;
     particle->instantiate = &instantiate;

particles/ramp.c

@@ -61,7 +61,7 @@ instantiate(const struct particle *particle, const struct tag_set *tags)
 struct particle *
 particle_ramp_new(const char *tag, struct particle *particles[], size_t count)
 {
-    struct particle *particle = particle_common_new(0, 0);
+    struct particle *particle = particle_common_new(0, 0, NULL);
     particle->destroy = &particle_destroy;
     particle->instantiate = &instantiate;