DummyPlugin: fix events emits for call-removed, origin-*

This fixes this two issues:
- Emit the events origin-removed, origin-added when required.

- Remove call immediately when disconnected and emit events:
  By using `g_idle_add ()` we can't be sure when the call is actually
  removed and could stay potentionaly for evere, as long the main loop is
  busy. This can lead to unexpected behavior. If the calls shouldn't be
  freed then it's required to increase the ref count. This is similar how
  the `remove` event works in a `GtkContainer`.

plugins/dummy/calls-dummy-provider.c

@@ -135,10 +135,19 @@ get_property (GObject      *object,
 static void
 dispose (GObject *object)
 {
+  gpointer origin;
+  GList *next;
   CallsDummyProvider *self = CALLS_DUMMY_PROVIDER (object);
 
-  g_list_free_full (self->origins, g_object_unref);
-  self->origins = NULL;
+  while (self->origins != NULL) {
+    origin = self->origins->data;
+    next = self->origins->next;
+    g_list_free_1 (self->origins);
+    self->origins = next;
+
+    g_signal_emit_by_name (self, "origin-removed", origin);
+    g_object_unref (origin);
+  }
 
   G_OBJECT_CLASS (calls_dummy_provider_parent_class)->dispose (object);
 }
@@ -181,8 +190,10 @@ void
 calls_dummy_provider_add_origin (CallsDummyProvider *self,
                                  const gchar        *name)
 {
-  self->origins = g_list_append (self->origins,
-                                 calls_dummy_origin_new (name));
+  CallsDummyOrigin *origin = calls_dummy_origin_new (name);
+  self->origins = g_list_append (self->origins, origin);
+
+  g_signal_emit_by_name (CALLS_PROVIDER (self), "origin-added", CALLS_ORIGIN (origin));
 }