[FIX] web: add missing icon, add warning, fix deferred

[FIX] web: add missing icon, add warning, fix deferred

* ir_actions_common should return a deferred : some widgets
  do not return a deferred in start, so it could be undefined.
  it now is always a deferred.
* add icon for diagram view + breadcrumb support. diagram view
  is so rare that it wasn't tested in the client refactoring.
  This patch adds an icon for diagram view, and better support for
  breadcrumbs
* add warning in debug mode print workflow: when no record is
  selected, display a warning instead of failing silently