[CLEAN] website_event_track: cleanind / migration to new api of the module
- removed event.tag and event.track.stage models
- cleaning / linting
- fixed kanban view of tracks
[FIX] web_tip: better event handling

* Override message_fetch from mail.Thread in a dedicated limk module (mail_tip)
and fire an event when the messages are loaded. This is necessary for tips on
the chatter.
* Override render_value form web.form.FieldStatus: Call reposition() when a
FieldStatus object is done rendering.
* Tip.reposition() method
* Handle web bus resize event