event-dispatcher: log event and hook names and chains

- Add a new variable "name" in WpEventHook and use it to log all the
  hooks(by name) picked up in _push_event(). This gives a clear picture
  if hook is registered for a given event.
- Form a name for an event and a chain of events for an event run, log
  both of them. This gives a clear picture of the events executed and
  order in which they are dispatched.
- Similarly build hooks chain and print it in _source_dispatch(), this
  gives a clear picture of the hooks picked and the order in which they
  are dispatched.
- Log only the dispatchable(with hooks) events, this de-clutters
  the log messages.

src/scripts/create-item.lua

@@ -62,6 +62,7 @@ end
 AsyncEventHook {
   priority = 10,
   type = "on-event",
+  name = "create-item-node-added",
   interests = {
     EventInterest {
       Constraint { "event.type", "=", "object-added" },
@@ -139,6 +140,7 @@ AsyncEventHook {
 SimpleEventHook {
   priority = 10,
   type = "on-event",
+  name = "create-item-node-removed",
   interests = {
     EventInterest {
       Constraint { "event.type", "=", "object-removed" },