[FIX] load view from file shall not raise an exception

In --dev mode, when a view can't be loaded from the file in spite of
being referenced in field `arch_fs`, the current behavior is to raise
an exception. In most cases, developpers don't want the view to fail
so the behavior has been changed in favor of a logger warning and
a fallback to `arch_db`.
[FIX] website_mail: "save and continue" button
[CLEAN] website_event_track, event: cleaning of website_event_track module:
- linter
- move event.tag model to event
- udpate me